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Generic algorithms perform an amazing task: due to the strenght of templates
algorithms could be developed that can be applied to a wide range of different
data types while maintaining type safety. The prototypical example of this is
the sort
generic algorithm (cf. section 19.1.58). To contrast: while
C requires programmers to write callback functions in which type-unsafe
void const *
parameters have to be used, internally forcing the programmer
to use casts, the STL sort
algorithm allows the programmer in many cases
to state something akin to
sort(first-element, last-element)to sort a series of elements in a type-safe way.
Generic algoritms should be used wherever possible. Avoid the urge to design your own code for commonly encountered algorithms. Make it a habit to first thoroughly search the generic algorithms for an available candidate. The generic algorithms should become your weapon of choice when writing code: acquire full familiarity with them and turn their use into your `second nature'.
The following sections describe the STL's generic algorithms in alphabetical order. For each algorithm the following information is provided:
Type
is used to specify a
generic data type. Also, the particular type of iterator (see section
18.2) that is required is mentioned, as well as other generic types
that might be required (e.g., performing BinaryOperations
, like
plus<Type>()
).
Almost every generic algorithm expects an iterator range
[first, last)
,
defining the range of elements on which the algorithm operates. The iterators
point to objects or values. When an iterator points to a Type
value or
object, function objects used by the algorithms usually receive Type const
&
objects or values: function objects can therefore not modify the objects
they receive as their arguments. This does not hold true for
modifying generic algorithms, which are (of course) able to
modify the objects they operate upon.
Generic algorithms may be categorized. In the C++ Annotations the following categories of generic algorithms are distinguished:
Requires:#include <algorithm>
equal(); includes(); lexicographical_compare(); max(); min(); mismatch();
Requires:#include <algorithm>
copy(); copy_backward(); partial_sort_copy(); remove_copy(); remove_copy_if(); replace_copy(); replace_copy_if(); reverse_copy(); rotate_copy(); unique_copy();
Requires:
#include <algorithm>
Requires:
#include <algorithm>
Requires:
#include <algorithm>
Requires:#include <numeric>
accumulate(); adjacent_difference(); inner_product(); partial_sum();
Requires:#include <algorithm>
adjacent_find(); binary_search(); equal_range(); find(); find_end(); find_first_of(); find_if(); lower_bound(); max_element(); min_element(); search(); search_n(); set_difference(); set_intersection(); set_symmetric_difference(); set_union(); upper_bound();
Requires:#include <algorithm>
inplace_merge(); iter_swap(); merge(); next_permutation(); nth_element(); partial_sort(); partial_sort_copy(); partition(); prev_permutation(); random_shuffle(); remove(); remove_copy(); remove_copy_if(); remove_if(); reverse(); reverse_copy(); rotate(); rotate_copy(); sort(); stable_partition(); stable_sort(); swap(); unique();
Requires:#include <algorithm>
for_each(); replace(); replace_copy(); replace_copy_if(); replace_if(); transform(); unique_copy();
#include <numeric>
Type accumulate(InputIterator first, InputIterator last,
Type init);
Type accumulate(InputIterator first, InputIterator
last, Type init,
BinaryOperation op);
operator+()
is applied to all
elements implied by the iterator range and to the initial value init
.
The resulting value is returned.
op()
is applied to
all elements implied by the iterator range and to the initial value init
,
and the resulting value is returned.
#include <numeric> #include <vector> #include <iostream> using namespace std; int main() { int ia[] = {1, 2, 3, 4}; vector<int> iv(ia, ia + 4); cout << "Sum of values: " << accumulate(iv.begin(), iv.end(), int()) << endl << "Product of values: " << accumulate(iv.begin(), iv.end(), int(1), multiplies<int>()) << endl; return 0; } /* Generated output: Sum of values: 10 Product of values: 24 */
#include <numeric>
OutputIterator adjacent_difference(InputIterator first,
InputIterator last, OutputIterator result);
OutputIterator adjacent_difference(InputIterator first,
InputIterator last, OutputIterator result, BinaryOperation
op);
op
applied to the
corresponding element in the input range (left operand) and its previous
element (right operand).
#include <numeric> #include <vector> #include <iostream> using namespace std; int main() { int ia[] = {1, 2, 5, 10}; vector<int> iv(ia, ia + 4); vector<int> ov(iv.size()); adjacent_difference(iv.begin(), iv.end(), ov.begin()); copy(ov.begin(), ov.end(), ostream_iterator<int>(cout, " ")); cout << endl; adjacent_difference(iv.begin(), iv.end(), ov.begin(), minus<int>()); copy(ov.begin(), ov.end(), ostream_iterator<int>(cout, " ")); cout << endl; return 0; } /* generated output: 1 1 3 5 1 1 3 5 */
#include <algorithm>
ForwardIterator adjacent_find(ForwardIterator first,
ForwardIterator last);
OutputIterator adjacent_find(ForwardIterator first,
ForwardIterator last,
Predicate pred);
last
is returned.
pred
returns true
is returned. If no such element exists,
last
is returned.
#include <algorithm> #include <string> #include <iostream> class SquaresDiff { size_t d_minimum; public: SquaresDiff(size_t minimum) : d_minimum(minimum) {} bool operator()(size_t first, size_t second) { return second * second - first * first >= d_minimum; } }; using namespace std; int main() { string sarr[] = { "Alpha", "bravo", "charley", "delta", "echo", "echo", "foxtrot", "golf" }; string *last = sarr + sizeof(sarr) / sizeof(string); string *result = adjacent_find(sarr, last); cout << *result << endl; result = adjacent_find(++result, last); cout << "Second time, starting from the next position:\n" << ( result == last ? "** No more adjacent equal elements **" : "*result" ) << endl; size_t iv[] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10}; size_t *ilast = iv + sizeof(iv) / sizeof(size_t); size_t *ires = adjacent_find(iv, ilast, SquaresDiff(10)); cout << "The first numbers for which the squares differ at least 10: " << *ires << " and " << *(ires + 1) << endl; return 0; } /* Generated output: echo Second time, starting from the next position: ** No more adjacent equal elements ** The first numbers for which the squares differ at least 10: 5 and 6 */
#include <algorithm>
bool binary_search(ForwardIterator first,
ForwardIterator last,
Type const &value);
bool binary_search(ForwardIterator first,
ForwardIterator last,
Type const &value, Comparator comp);
value
is looked up using binary
search in the range of elements implied by the iterator range [first,
last)
. The elements in the range must have been sorted by the
Type::operator<()
function. True
is returned if the element was found,
false
otherwise.
value
is looked up using binary
search in the range of elements implied by the iterator range [first,
last)
. The elements in the range must have been sorted by the
Comparator
function object. True
is returned if the element was found,
false
otherwise.
#include <algorithm> #include <string> #include <iostream> #include <functional> using namespace std; int main() { string sarr[] = { "alpha", "bravo", "charley", "delta", "echo", "foxtrot", "golf", "hotel" }; string *last = sarr + sizeof(sarr) / sizeof(string); bool result = binary_search(sarr, last, "foxtrot"); cout << (result ? "found " : "didn't find ") << "foxtrot" << endl; reverse(sarr, last); // reverse the order of elements // binary search now fails: result = binary_search(sarr, last, "foxtrot"); cout << (result ? "found " : "didn't find ") << "foxtrot" << endl; // ok when using appropriate // comparator: result = binary_search(sarr, last, "foxtrot", greater<string>()); cout << (result ? "found " : "didn't find ") << "foxtrot" << endl; return 0; } /* Generated output: found foxtrot didn't find foxtrot found foxtrot */
#include <algorithm>
OutputIterator copy(InputIterator first,
InputIterator last,
OutputIterator destination);
[first, last)
is copied to an output range, starting at
destination
using the assignment operator of the underlying data
type. The return value is the OutputIterator pointing just beyond the last
element that was copied to the destination range (so, `last' in the destination
range is returned).
copy()
. It uses an ostream_iterator
for
string
objects. This iterator will write the string
values to the
specified ostream
(i.e., cout
), separating the values by the specified
separation string (i.e., " "
).
#include <algorithm> #include <string> #include <iostream> #include <iterator> using namespace std; int main() { string sarr[] = { "alpha", "bravo", "charley", "delta", "echo", "foxtrot", "golf", "hotel" }; string *last = sarr + sizeof(sarr) / sizeof(string); copy(sarr + 2, last, sarr); // move all elements two positions left // copy to cout using an ostream_iterator // for strings, copy(sarr, last, ostream_iterator<string>(cout, " ")); cout << endl; return 0; } /* Generated output: charley delta echo foxtrot golf hotel golf hotel */
unique_copy()
#include <algorithm>
BidirectionalIterator copy_backward(InputIterator
first,
InputIterator last, BidirectionalIterator
last2);
[first, last)
are copied from the element at position last - 1
until (and including) the element at position first
to the element range,
ending at position last2 - 1
using the assignment operator of the
underlying data type. The destination range is therefore [last2 - (last
- first), last2)
.
The return value is the BidirectionalIterator pointing to the last element that
was copied to the destination range (so, `first' in the destination range, pointed to by last2 - (last - first)
, is returned).
#include <algorithm> #include <string> #include <iostream> #include <iterator> using namespace std; int main() { string sarr[] = { "alpha", "bravo", "charley", "delta", "echo", "foxtrot", "golf", "hotel" }; string *last = sarr + sizeof(sarr) / sizeof(string); copy ( copy_backward(sarr + 3, last, last - 3), last, ostream_iterator<string>(cout, " ") ); cout << endl; return 0; } /* Generated output: golf hotel foxtrot golf hotel foxtrot golf hotel */
#include <algorithm>
size_t count(InputIterator first, InputIterator last, Type
const &value);
value
occurs in the iterator range
[first, last)
is returned. Use Type::operator==()
to determine
whether value
is equal to an element in the iterator range.
#include <algorithm> #include <iostream> using namespace std; int main() { int ia[] = {1, 2, 3, 4, 3, 4, 2, 1, 3}; cout << "Number of times the value 3 is available: " << count(ia, ia + sizeof(ia) / sizeof(int), 3) << endl; return 0; } /* Generated output: Number of times the value 3 is available: 3 */
#include <algorithm>
size_t count_if(InputIterator first,
InputIterator last,
Predicate predicate);
#include <algorithm> #include <iostream> class Odd { public: bool operator()(int value) { return value & 1; } }; using namespace std; int main() { int ia[] = {1, 2, 3, 4, 3, 4, 2, 1, 3}; cout << "The number of odd values in the array is: " << count_if(ia, ia + sizeof(ia) / sizeof(int), Odd()) << endl; return 0; } /* Generated output: The number of odd values in the array is: 5 */
#include <algorithm>
bool equal(InputIterator first, InputIterator
last, InputIterator
otherFirst);
bool equal(InputIterator first, InputIterator last,
InputIterator
otherFirst, BinaryPredicate pred);
[first,
last)
are compared to a range of equal length starting at otherFirst
. The
function returns true
if the visited elements in both ranges are equal
pairwise. The ranges need not be of equal length, only the elements in the
indicated range are considered (and must be available).
[first, last)
are compared to a range of equal length starting at
otherFirst
. The function returns true
if the binary predicate, applied
to all corresponding elements in both ranges returns true
for every pair
of corresponding elements. The ranges need not be of equal length, only the
elements in the indicated range are considered (and must be available).
#include <algorithm> #include <string> #include <iostream> class CaseString { public: bool operator()(std::string const &first, std::string const &second) const { return !strcasecmp(first.c_str(), second.c_str()); } }; using namespace std; int main() { string first[] = { "Alpha", "bravo", "Charley", "delta", "Echo", "foxtrot", "Golf", "hotel" }; string second[] = { "alpha", "bravo", "charley", "delta", "echo", "foxtrot", "golf", "hotel" }; string *last = first + sizeof(first) / sizeof(string); cout << "The elements of `first' and `second' are pairwise " << (equal(first, last, second) ? "equal" : "not equal") << endl << "compared case-insensitively, they are " << ( equal(first, last, second, CaseString()) ? "equal" : "not equal" ) << endl; return 0; } /* Generated output: The elements of `first' and `second' are pairwise not equal compared case-insensitively, they are equal */
#include <algorithm>
pair<ForwardIterator, ForwardIterator>
equal_range(ForwardIterator
first, ForwardIterator last, Type const &value);
pair<ForwardIterator, ForwardIterator>
equal_range(ForwardIterator
first, ForwardIterator last, Type const &value,
Compare comp);
map
(section 12.3.6) and multimap
(section
12.3.7)):
operator<()
of the data type to which the iterators point was used to
sort the elements in the provided range), a pair of iterators is returned
representing the return value of, respectively, lower_bound()
(returning
the first element that is not smaller than the provided reference value, see
section 19.1.25) and upper_bound()
(returning the first element
beyond the provided reference value, see section 19.1.66).
comp
function object was used to sort the elements in the provided
range), a pair of iterators is returned representing the return values of,
respectively, the functions lower_bound()
(section 19.1.25) and
upper_bound()
(section 19.1.66).
#include <algorithm> #include <functional> #include <iterator> #include <iostream> using namespace std; int main() { int range[] = {1, 3, 5, 7, 7, 9, 9, 9}; size_t const size = sizeof(range) / sizeof(int); pair<int *, int *> pi; pi = equal_range(range, range + size, 6); cout << "Lower bound for 6: " << *pi.first << endl; cout << "Upper bound for 6: " << *pi.second << endl; pi = equal_range(range, range + size, 7); cout << "Lower bound for 7: "; copy(pi.first, range + size, ostream_iterator<int>(cout, " ")); cout << endl; cout << "Upper bound for 7: "; copy(pi.second, range + size, ostream_iterator<int>(cout, " ")); cout << endl; sort(range, range + size, greater<int>()); cout << "Sorted in descending order\n"; copy(range, range + size, ostream_iterator<int>(cout, " ")); cout << endl; pi = equal_range(range, range + size, 7, greater<int>()); cout << "Lower bound for 7: "; copy(pi.first, range + size, ostream_iterator<int>(cout, " ")); cout << endl; cout << "Upper bound for 7: "; copy(pi.second, range + size, ostream_iterator<int>(cout, " ")); cout << endl; return 0; } /* Generated output: Lower bound for 6: 7 Upper bound for 6: 7 Lower bound for 7: 7 7 9 9 9 Upper bound for 7: 9 9 9 Sorted in descending order 9 9 9 7 7 5 3 1 Lower bound for 7: 7 7 5 3 1 Upper bound for 7: 5 3 1 */
#include <algorithm>
void fill(ForwardIterator first, ForwardIterator last, Type
const &value);
[first, last)
are initialized to value
, overwriting the previous
stored values.
#include <algorithm> #include <vector> #include <iterator> #include <iostream> using namespace std; int main() { vector<int> iv(8); fill(iv.begin(), iv.end(), 8); copy(iv.begin(), iv.end(), ostream_iterator<int>(cout, " ")); cout << endl; return 0; } /* Generated output: 8 8 8 8 8 8 8 8 */
#include <algorithm>
void fill_n(ForwardIterator first, Size n, Type
const &value);
n
elements starting at the element pointed to by
first
are initialized to value
, overwriting the previous
stored values.
#include <algorithm> #include <vector> #include <iterator> #include <iostream> using namespace std; int main() { vector<int> iv(8); fill_n(iv.begin() + 2, 4, 8); copy(iv.begin(), iv.end(), ostream_iterator<int>(cout, " ")); cout << endl; return 0; } /* Generated output: 0 0 8 8 8 8 0 0 */
#include <algorithm>
InputIterator find(InputIterator first,
InputIterator last, Type const &value);
value
is searched for in the range of the elements
implied by the iterator range [first, last)
. An iterator pointing to
the first element found is returned. If the element was not found, last
is
returned. The operator==()
of the underlying data type is used to
compare the elements.
#include <algorithm> #include <string> #include <iterator> #include <iostream> using namespace std; int main() { string sarr[] = { "alpha", "bravo", "charley", "delta", "echo" }; string *last = sarr + sizeof(sarr) / sizeof(string); copy ( find(sarr, last, "delta"), last, ostream_iterator<string>(cout, " ") ); cout << endl; if (find(sarr, last, "india") == last) { cout << "`india' was not found in the range\n"; copy(sarr, last, ostream_iterator<string>(cout, " ")); cout << endl; } return 0; } /* Generated output: delta echo `india' was not found in the range alpha bravo charley delta echo */
#include <algorithm>
ForwardIterator1 find_end(ForwardIterator1 first1,
ForwardIterator1 last1,
ForwardIterator2 first2, ForwardIterator2 last2)
ForwardIterator1 find_end(ForwardIterator1 first1,
ForwardIterator1 last1,
ForwardIterator2 first2, ForwardIterator2 last2,
BinaryPredicate pred)
[first1, last1)
is searched for the last occurrence of the sequence of
elements implied by [first2, last2)
. If the sequence [first2,
last2)
is not found, last1
is returned, otherwise an iterator pointing to
the first element of the matching sequence is returned. The operator==()
of the underlying data type is used to compare the elements in the two
sequences.
[first1, last1)
is searched for the last occurrence of the sequence of
elements implied by [first2, last2)
. If the sequence [first2,
last2)
is not found, last1
is returned, otherwise an iterator pointing to
the first element of the matching sequence is returned. The provided binary
predicate is used to compare the elements in the two sequences.
#include <algorithm> #include <string> #include <iterator> #include <iostream> class Twice { public: bool operator()(size_t first, size_t second) const { return first == (second << 1); } }; using namespace std; int main() { string sarr[] = { "alpha", "bravo", "charley", "delta", "echo", "foxtrot", "golf", "hotel", "foxtrot", "golf", "hotel", "india", "juliet", "kilo" }; string search[] = { "foxtrot", "golf", "hotel" }; string *last = sarr + sizeof(sarr) / sizeof(string); copy ( find_end(sarr, last, search, search + 3), // sequence starting last, ostream_iterator<string>(cout, " ") // at 2nd 'foxtrot' ); cout << endl; size_t range[] = {2, 4, 6, 8, 10, 4, 6, 8, 10}; size_t nrs[] = {2, 3, 4}; copy // sequence of values starting at last sequence ( // of range[] that are twice the values in nrs[] find_end(range, range + 9, nrs, nrs + 3, Twice()), range + 9, ostream_iterator<size_t>(cout, " ") ); cout << endl; return 0; } /* Generated output: foxtrot golf hotel india juliet kilo 4 6 8 10 */
#include <algorithm>
ForwardIterator1 find_first_of(ForwardIterator1 first1,
ForwardIterator1 last1, ForwardIterator2 first2, ForwardIterator2 last2)
ForwardIterator1 find_first_of(ForwardIterator1 first1,
ForwardIterator1 last1, ForwardIterator2 first2, ForwardIterator2 last2,
BinaryPredicate pred)
[first1, last1)
is searched for the first occurrence of an element in
the sequence of elements implied by [first2, last2)
. If no element in
the sequence [first2, last2)
is found, last1
is returned, otherwise
an iterator pointing to the first element in [first1, last1)
that is
equal to an element in [first2, last2)
is returned. The
operator==()
of the underlying data type is used to compare the elements
in the two sequences.
[first1, first1)
is searched for the first occurrence of an element in
the sequence of elements implied by [first2, last2)
. Each element in
the range [first1, last1)
is compared to each element in the range
[first2, last2)
, and an iterator to the first element in
[first1, last1)
for which the binary predicate pred
(receiving an
the element out of the range [first1, last1)
and an element from the
range [first2, last2)
) returns true
is returned. Otherwise,
last1
is returned.
#include <algorithm> #include <string> #include <iterator> #include <iostream> class Twice { public: bool operator()(size_t first, size_t second) const { return first == (second << 1); } }; using namespace std; int main() { string sarr[] = { "alpha", "bravo", "charley", "delta", "echo", "foxtrot", "golf", "hotel", "foxtrot", "golf", "hotel", "india", "juliet", "kilo" }; string search[] = { "foxtrot", "golf", "hotel" }; string *last = sarr + sizeof(sarr) / sizeof(string); copy ( // sequence starting find_first_of(sarr, last, search, search + 3), // at 1st 'foxtrot' last, ostream_iterator<string>(cout, " ") ); cout << endl; size_t range[] = {2, 4, 6, 8, 10, 4, 6, 8, 10}; size_t nrs[] = {2, 3, 4}; copy // sequence of values starting at first sequence ( // of range[] that are twice the values in nrs[] find_first_of(range, range + 9, nrs, nrs + 3, Twice()), range + 9, ostream_iterator<size_t>(cout, " ") ); cout << endl; return 0; } /* Generated output: foxtrot golf hotel foxtrot golf hotel india juliet kilo 4 6 8 10 4 6 8 10 */
#include <algorithm>
InputIterator find_if(InputIterator first,
InputIterator last, Predicate pred);
[first, last)
for which the (unary)
predicate pred
returns true
is returned. If the element was not found,
last
is returned.
#include <algorithm> #include <string> #include <iterator> #include <iostream> class CaseName { std::string d_string; public: CaseName(char const *str): d_string(str) {} bool operator()(std::string const &element) { return !strcasecmp(element.c_str(), d_string.c_str()); } }; using namespace std; int main() { string sarr[] = { "Alpha", "Bravo", "Charley", "Delta", "Echo" }; string *last = sarr + sizeof(sarr) / sizeof(string); copy ( find_if(sarr, last, CaseName("charley")), last, ostream_iterator<string>(cout, " ") ); cout << endl; if (find_if(sarr, last, CaseName("india")) == last) { cout << "`india' was not found in the range\n"; copy(sarr, last, ostream_iterator<string>(cout, " ")); cout << endl; } return 0; } /* Generated output: Charley Delta Echo `india' was not found in the range Alpha Bravo Charley Delta Echo */
#include <algorithm>
Function for_each(ForwardIterator first,
ForwardIterator last, Function func);
[first, last)
is passed in turn as a reference to the function (or
function object) func
. The function may modify the elements it receives
(as the used iterator is a forward iterator). Alternatively, if the elements
should be transformed, transform()
(see section 19.1.63) can be
used. The function itself or a copy of the provided function object is
returned: see the example below, in which an extra argument list is added to
the for_each()
call, which argument is eventually also passed to the
function given to for_each()
. Within for_each()
the return value of
the function that is passed to it is ignored.
#include <algorithm> #include <string> #include <iostream> #include <cctype> void lowerCase(char &c) // `c' *is* modified { c = static_cast<char>(tolower(c)); } // `str' is *not* modified void capitalizedOutput(std::string const &str) { char *tmp = strcpy(new char[str.size() + 1], str.c_str()); std::for_each(tmp + 1, tmp + str.size(), lowerCase); tmp[0] = toupper(*tmp); std::cout << tmp << " "; delete tmp; }; using namespace std; int main() { string sarr[] = { "alpha", "BRAVO", "charley", "DELTA", "echo", "FOXTROT", "golf", "HOTEL" }; string *last = sarr + sizeof(sarr) / sizeof(string); for_each(sarr, last, capitalizedOutput)("that's all, folks"); cout << endl; return 0; } /* Generated output: Alpha Bravo Charley Delta Echo Foxtrot Golf Hotel That's all, folks */
#include <algorithm> #include <string> #include <iostream> #include <cctype> void lowerCase(char &c) { c = tolower(c); } class Show { int d_count; public: Show() : d_count(0) {} void operator()(std::string &str) { std::for_each(str.begin(), str.end(), lowerCase); str[0] = toupper(str[0]); // here assuming str.length() std::cout << ++d_count << " " << str << "; "; } int count() const { return d_count; } }; using namespace std; int main() { string sarr[] = { "alpha", "BRAVO", "charley", "DELTA", "echo", "FOXTROT", "golf", "HOTEL" }; string *last = sarr + sizeof(sarr) / sizeof(string); cout << for_each(sarr, last, Show()).count() << endl; return 0; } /* Generated output (all on a single line): 1 Alpha; 2 Bravo; 3 Charley; 4 Delta; 5 Echo; 6 Foxtrot; 7 Golf; 8 Hotel; 8 */
for_each
algorithm may be used with
functions defining const
and non-const
parameters. Also, see section
19.1.63 for differences between the for_each()
and transform()
generic algorithms.
The for_each()
algorithm cannot directly be used (i.e., by passing
*this
as the function object argument) inside a member function to modify
its own object as the for_each()
algorithm first creates its own copy of
the passed function object. A
wrapper class whose constructor accepts a
pointer or reference to the current object and possibly to one of its member
functions solves this problem. In section 23.8 the construction
of such wrapper classes is described.
#include <algorithm>
void generate(ForwardIterator first,
ForwardIterator last,
Generator generator);
[first,
last)
are initialized by the return value of generator
, which can be a
function or function object. Generator::operator()()
does not receive
any arguments. The example uses a well-known fact from algebra: in order to
obtain the square of n + 1
, add 1 + 2 * n
to n * n
.
#include <algorithm> #include <vector> #include <iterator> #include <iostream> class NaturalSquares { size_t d_newsqr; size_t d_last; public: NaturalSquares(): d_newsqr(0), d_last(0) {} size_t operator()() { // using: (a + 1)^2 == a^2 + 2*a + 1 return d_newsqr += (d_last++ << 1) + 1; } }; using namespace std; int main() { vector<size_t> uv(10); generate(uv.begin(), uv.end(), NaturalSquares()); copy(uv.begin(), uv.end(), ostream_iterator<int>(cout, " ")); cout << endl; return 0; } /* Generated output: 1 4 9 16 25 36 49 64 81 100 */
#include <algorithm>
void generate_n(ForwardIterator first, Size n,
Generator generator);
n
elements starting at the element pointed to by
iterator first
are initialized by the return value of generator
,
which can be a function or function object.
#include <algorithm> #include <vector> #include <iterator> #include <iostream> class NaturalSquares { size_t d_newsqr; size_t d_last; public: NaturalSquares(): d_newsqr(0), d_last(0) {} size_t operator()() { // using: (a + 1)^2 == a^2 + 2*a + 1 return d_newsqr += (d_last++ << 1) + 1; } }; using namespace std; int main() { vector<size_t> uv(10); generate_n(uv.begin(), 5, NaturalSquares()); copy(uv.begin(), uv.end(), ostream_iterator<int>(cout, " ")); cout << endl; return 0; } /* Generated output: 1 4 9 16 25 0 0 0 0 0 */
#include <algorithm>
bool includes(InputIterator1 first1, InputIterator1 last1,
InputIterator2 first2, InputIterator2 last2);
bool includes(InputIterator1 first1, InputIterator1 last1,
InputIterator2 first2, InputIterator2 last2, Compare comp);
[first1, last1)
and [first2, last2)
should have been
sorted using the operator<()
of the data type to which the iterators
point. The function returns true
if every element in the second sequence
[first2, second2)
is contained in the first sequence [first1,
second1)
(the second range is a subset of the first range).
[first1, last1)
and [first2, last2)
should have been
sorted using the comp
function object. The function returns true
if
every element in the second sequence [first2, second2)
is contained in
the first seqence [first1, second1)
(the second range is a subset of
the first range).
#include <algorithm> #include <string> #include <iostream> class CaseString { public: bool operator()(std::string const &first, std::string const &second) const { return !strcasecmp(first.c_str(), second.c_str()); } }; using namespace std; int main() { string first1[] = { "alpha", "bravo", "charley", "delta", "echo", "foxtrot", "golf", "hotel" }; string first2[] = { "Alpha", "bravo", "Charley", "delta", "Echo", "foxtrot", "Golf", "hotel" }; string second[] = { "charley", "foxtrot", "hotel" }; size_t n = sizeof(first1) / sizeof(string); cout << "The elements of `second' are " << (includes(first1, first1 + n, second, second + 3) ? "" : "not") << " contained in the first sequence:\n" "second is a subset of first1\n"; cout << "The elements of `first1' are " << (includes(second, second + 3, first1, first1 + n) ? "" : "not") << " contained in the second sequence\n"; cout << "The elements of `second' are " << (includes(first2, first2 + n, second, second + 3) ? "" : "not") << " contained in the first2 sequence\n"; cout << "Using case-insensitive comparison,\n" "the elements of `second' are " << (includes(first2, first2 + n, second, second + 3, CaseString()) ? "" : "not") << " contained in the first2 sequence\n"; return 0; } /* Generated output: The elements of `second' are contained in the first sequence: second is a subset of first1 The elements of `first1' are not contained in the second sequence The elements of `second' are not contained in the first2 sequence Using case-insensitive comparison, the elements of `second' are contained in the first2 sequence */
#include <numeric>
Type inner_product(InputIterator1 first1,
InputIterator1 last1,
InputIterator2 first2, Type init);
Type inner_product(InputIterator1 first1,
InputIterator1 last1,
InputIterator2 first2, Type init, BinaryOperator1 op1,
BinaryOperator2 op2);
[first1, last1)
and the same number of
elements starting at the element pointed to by first2
are added to init
, and this sum is returned. The function uses the
operator+()
and operator*()
of the data type to which the iterators
point.
op1
instead of the
default addition operator, and binary operator op2
instead of the default
multiplication operator are applied to all pairwise elements implied by the
range [first1, last1)
and the same number of elements starting at the
element pointed to by first2
. The final result is returned.
#include <numeric> #include <algorithm> #include <iterator> #include <iostream> #include <string> class Cat { std::string d_sep; public: Cat(std::string const &sep) : d_sep(sep) {} std::string operator() (std::string const &s1, std::string const &s2) const { return s1 + d_sep + s2; } }; using namespace std; int main() { size_t ia1[] = {1, 2, 3, 4, 5, 6, 7}; size_t ia2[] = {7, 6, 5, 4, 3, 2, 1}; size_t init = 0; cout << "The sum of all squares in "; copy(ia1, ia1 + 7, ostream_iterator<size_t>(cout, " ")); cout << "is " << inner_product(ia1, ia1 + 7, ia1, init) << endl; cout << "The sum of all cross-products in "; copy(ia1, ia1 + 7, ostream_iterator<size_t>(cout, " ")); cout << " and "; copy(ia2, ia2 + 7, ostream_iterator<size_t>(cout, " ")); cout << "is " << inner_product(ia1, ia1 + 7, ia2, init) << endl; string names1[] = {"Frank", "Karel", "Piet"}; string names2[] = {"Brokken", "Kubat", "Plomp"}; cout << "A list of all combined names in "; copy(names1, names1 + 3, ostream_iterator<string>(cout, " ")); cout << "and\n"; copy(names2, names2 + 3, ostream_iterator<string>(cout, " ")); cout << "is:" << inner_product(names1, names1 + 3, names2, string("\t"), Cat("\n\t"), Cat(" ")) << endl; return 0; } /* Generated output: The sum of all squares in 1 2 3 4 5 6 7 is 140 The sum of all cross-products in 1 2 3 4 5 6 7 and 7 6 5 4 3 2 1 is 84 A list of all combined names in Frank Karel Piet and Brokken Kubat Plomp is: Frank Brokken Karel Kubat Piet Plomp */
#include <algorithm>
void inplace_merge(BidirectionalIterator first,
BidirectionalIterator
middle, BidirectionalIterator last);
void inplace_merge(BidirectionalIterator first,
BidirectionalIterator
middle, BidirectionalIterator last, Compare comp);
[first,
middle)
and [middle, last)
are merged, keeping a sorted list (using the
operator<()
of the data type to which the iterators point). The final
series is stored in the range [first, last)
.
[first,
middle)
and [middle, last)
are merged, keeping a sorted list (using the
boolean result of the binary comparison operator comp
). The final series
is stored in the range [first, last)
.
#include <algorithm> #include <string> #include <iterator> #include <iostream> class CaseString { public: bool operator()(std::string const &first, std::string const &second) const { return strcasecmp(first.c_str(), second.c_str()) < 0; } }; using namespace std; int main() { string range[] = { "alpha", "charley", "echo", "golf", "bravo", "delta", "foxtrot", }; inplace_merge(range, range + 4, range + 7); copy(range, range + 7, ostream_iterator<string>(cout, " ")); cout << endl; string range2[] = { "ALFA", "CHARLEY", "DELTA", "foxtrot", "hotel", "bravo", "ECHO", "GOLF" }; inplace_merge(range2, range2 + 5, range2 + 8, CaseString()); copy(range2, range2 + 8, ostream_iterator<string>(cout, " ")); cout << endl; return 0; } /* Generated output: alpha bravo charley delta echo foxtrot golf ALFA bravo CHARLEY DELTA ECHO foxtrot GOLF hotel */
#include <algorithm>
void iter_swap(ForwardIterator1 iter1,
ForwardIterator2 iter2);
iter1
and iter2
are
swapped.
#include <algorithm> #include <iterator> #include <iostream> #include <string> using namespace std; int main() { string first[] = {"alpha", "bravo", "charley"}; string second[] = {"echo", "foxtrot", "golf"}; size_t const n = sizeof(first) / sizeof(string); cout << "Before:\n"; copy(first, first + n, ostream_iterator<string>(cout, " ")); cout << endl; copy(second, second + n, ostream_iterator<string>(cout, " ")); cout << endl; for (size_t idx = 0; idx < n; ++idx) iter_swap(first + idx, second + idx); cout << "After:\n"; copy(first, first + n, ostream_iterator<string>(cout, " ")); cout << endl; copy(second, second + n, ostream_iterator<string>(cout, " ")); cout << endl; return 0; } /* Generated output: Before: alpha bravo charley echo foxtrot golf After: echo foxtrot golf alpha bravo charley */
#include <algorithm>
bool lexicographical_compare(InputIterator1 first1,
InputIterator1 last1,
InputIterator2 first2, InputIterator2 last2);
bool lexicographical_compare(InputIterator1 first1,
InputIterator1 last1,
InputIterator2 first2, InputIterator2 last2,
Compare comp);
[first1, last1)
and [first2, last2)
are
compared. The function returns
true
operator<()
of the underlying data type),
last1
is reached, but last2
isn't reached yet.
false
is
returned:
operator<()
of the data type to which the iterators point, reversing the operands),
last2
is reached, but last1
isn't reached yet,
last1
and last2
are reached.
comp
is used instead of
operator<()
of the data type to which the iterators point.
#include <algorithm> #include <iterator> #include <iostream> #include <string> class CaseString { public: bool operator()(std::string const &first, std::string const &second) const { return strcasecmp(first.c_str(), second.c_str()) < 0; } }; using namespace std; int main() { string word1 = "hello"; string word2 = "help"; cout << word1 << " is " << ( lexicographical_compare(word1.begin(), word1.end(), word2.begin(), word2.end()) ? "before " : "beyond or at " ) << word2 << " in the alphabet\n"; cout << word1 << " is " << ( lexicographical_compare(word1.begin(), word1.end(), word1.begin(), word1.end()) ? "before " : "beyond or at " ) << word1 << " in the alphabet\n"; cout << word2 << " is " << ( lexicographical_compare(word2.begin(), word2.end(), word1.begin(), word1.end()) ? "before " : "beyond or at " ) << word1 << " in the alphabet\n"; string one[] = {"alpha", "bravo", "charley"}; string two[] = {"ALPHA", "BRAVO", "DELTA"}; copy(one, one + 3, ostream_iterator<string>(cout, " ")); cout << " is ordered " << ( lexicographical_compare(one, one + 3, two, two + 3, CaseString()) ? "before " : "beyond or at " ); copy(two, two + 3, ostream_iterator<string>(cout, " ")); cout << endl << "using case-insensitive comparisons.\n"; return 0; } /* Generated output: hello is before help in the alphabet hello is beyond or at hello in the alphabet help is beyond or at hello in the alphabet alpha bravo charley is ordered before ALPHA BRAVO DELTA using case-insensitive comparisons. */
#include <algorithm>
ForwardIterator lower_bound(ForwardIterator first,
ForwardIterator last,
const Type &value);
ForwardIterator lower_bound(ForwardIterator first,
ForwardIterator last,
const Type &value, Compare comp);
[first, last)
are searched for the first element that is
not less than (i.e., greater than or equal to) value
. The returned
iterator marks the location in the sequence where value
can be inserted
without breaking the sorted order of the elements. The operator<()
of the
data type to which the iterators point is used. If no such element is found,
last
is returned.
[first, last)
must have been sorted using the comp
function
(-object). Each element in the range is compared to value
using the
comp
function. An iterator to the first element for which the binary
predicate comp
, applied to the elements of the range and value
,
returns false
is returned. If no such element is found, last
is
returned.
#include <algorithm> #include <iostream> #include <iterator> #include <functional> using namespace std; int main() { int ia[] = {10, 20, 30}; cout << "Sequence: "; copy(ia, ia + 3, ostream_iterator<int>(cout, " ")); cout << endl; cout << "15 can be inserted before " << *lower_bound(ia, ia + 3, 15) << endl; cout << "35 can be inserted after " << (lower_bound(ia, ia + 3, 35) == ia + 3 ? "the last element" : "???") << endl; iter_swap(ia, ia + 2); cout << "Sequence: "; copy(ia, ia + 3, ostream_iterator<int>(cout, " ")); cout << endl; cout << "15 can be inserted before " << *lower_bound(ia, ia + 3, 15, greater<int>()) << endl; cout << "35 can be inserted before " << (lower_bound(ia, ia + 3, 35, greater<int>()) == ia ? "the first element " : "???") << endl; return 0; } /* Generated output: Sequence: 10 20 30 15 can be inserted before 20 35 can be inserted after the last element Sequence: 30 20 10 15 can be inserted before 10 35 can be inserted before the first element */
#include <algorithm>
Type const &max(Type const &one, Type const &two);
Type const &max(Type const &one, Type const &two, Comparator
comp);
one
and two
is returned using the operator>()
of the data type to which
the iterators point.
one
is returned if the binary
predicate comp(one, two)
returns true
, otherwise two
is returned.
#include <algorithm> #include <iostream> #include <string> class CaseString { public: bool operator()(std::string const &first, std::string const &second) const { return strcasecmp(second.c_str(), first.c_str()) > 0; } }; using namespace std; int main() { cout << "Word '" << max(string("first"), string("second")) << "' is lexicographically last\n"; cout << "Word '" << max(string("first"), string("SECOND")) << "' is lexicographically last\n"; cout << "Word '" << max(string("first"), string("SECOND"), CaseString()) << "' is lexicographically last\n"; return 0; } /* Generated output: Word 'second' is lexicographically last Word 'first' is lexicographically last Word 'SECOND' is lexicographically last */
#include <algorithm>
ForwardIterator max_element(ForwardIterator first,
ForwardIterator last);
ForwardIterator max_element(ForwardIterator first,
ForwardIterator last,
Comparator comp);
[first, last)
is returned. The
operator<()
of the data type to which the iterators point is used.
operator<()
, the
binary predicate comp
is used to make the comparisons between the elements
implied by the iterator range [first, last)
. The element for which
comp
returns most often true
, compared with other elements, is
returned.
#include <algorithm> #include <iostream> class AbsValue { public: bool operator()(int first, int second) const { return abs(first) < abs(second); } }; using namespace std; int main() { int ia[] = {-4, 7, -2, 10, -12}; cout << "The max. int value is " << *max_element(ia, ia + 5) << endl; cout << "The max. absolute int value is " << *max_element(ia, ia + 5, AbsValue()) << endl; return 0; } /* Generated output: The max. int value is 10 The max. absolute int value is -12 */
#include <algorithm>
OutputIterator merge(InputIterator1 first1,
InputIterator1 last1,
InputIterator2 first2, InputIterator2 last2,
OutputIterator result);
OutputIterator merge(InputIterator1 first1,
InputIterator1 last1,
InputIterator2 first2, InputIterator2
last2, OutputIterator result,
Compare comp);
[first1,
last1)
and [first2, last2)
are merged, keeping a sorted list (using the
operator<()
of the data type to which the iterators point). The final
series is stored in the range starting at result
and ending just before
the OutputIterator
returned by the function.
[first1,
last1)
and [first2, last2)
are merged, keeping a sorted list (using the
boolean result of the binary comparison operator comp
). The final series
is stored in the range starting at result
and ending just before the
OutputIterator
returned by the function.
#include <algorithm> #include <string> #include <iterator> #include <iostream> class CaseString { public: bool operator()(std::string const &first, std::string const &second) const { return strcasecmp(first.c_str(), second.c_str()) < 0; } }; using namespace std; int main() { string range1[] = { // 5 elements "alpha", "bravo", "foxtrot", "hotel", "zulu" }; string range2[] = { // 4 elements "echo", "delta", "golf", "romeo" }; string result[5 + 4]; copy(result, merge(range1, range1 + 5, range2, range2 + 4, result), ostream_iterator<string>(cout, " ")); cout << endl; string range3[] = { "ALPHA", "bravo", "foxtrot", "HOTEL", "ZULU" }; string range4[] = { "delta", "ECHO", "GOLF", "romeo" }; copy(result, merge(range3, range3 + 5, range4, range4 + 4, result, CaseString()), ostream_iterator<string>(cout, " ")); cout << endl; return 0; } /* Generated output: alpha bravo echo delta foxtrot golf hotel romeo zulu ALPHA bravo delta ECHO foxtrot GOLF HOTEL romeo ZULU */
#include <algorithm>
Type const &min(Type const &one, Type const &two);
Type const &min(Type const &one, Type const &two, Comparator
comp);
one
and two
is returned using the operator<()
of the data type to which
the iterators point.
one
is returned if the binary
predicate comp(one, two)
returns false
, otherwise two
is returned.
#include <algorithm> #include <iostream> #include <string> class CaseString { public: bool operator()(std::string const &first, std::string const &second) const { return strcasecmp(second.c_str(), first.c_str()) > 0; } }; using namespace std; int main() { cout << "Word '" << min(string("first"), string("second")) << "' is lexicographically first\n"; cout << "Word '" << min(string("first"), string("SECOND")) << "' is lexicographically first\n"; cout << "Word '" << min(string("first"), string("SECOND"), CaseString()) << "' is lexicographically first\n"; return 0; } /* Generated output: Word 'first' is lexicographically first Word 'SECOND' is lexicographically first Word 'first' is lexicographically first */
#include <algorithm>
ForwardIterator min_element(ForwardIterator first,
ForwardIterator last);
ForwardIterator min_element(ForwardIterator first,
ForwardIterator last,
Comparator comp);
[first, last)
is returned using
operator<()
of the data type to which the iterators point.
operator<()
, the
binary predicate comp
is used to make the comparisons between the elements
implied by the iterator range [first, last)
. The element for which
comp
returns false
most often is returned.
#include <algorithm> #include <iostream> class AbsValue { public: bool operator()(int first, int second) const { return abs(first) < abs(second); } }; using namespace std; int main() { int ia[] = {-4, 7, -2, 10, -12}; cout << "The minimum int value is " << *min_element(ia, ia + 5) << endl; cout << "The minimum absolute int value is " << *min_element(ia, ia + 5, AbsValue()) << endl; return 0; } /* Generated output: The minimum int value is -12 The minimum absolute int value is -2 */
#include <algorithm>
pair<InputIterator1, InputIterator2>
mismatch(InputIterator1 first1,
InputIterator1 last1, InputIterator2 first2);
pair<InputIterator1, InputIterator2>
mismatch(InputIterator1 first1,
InputIterator1 last1, InputIterator2 first2,
Compare comp);
first1
and first2
are compared using the equality operator of the
data type to which the iterators point. Comparison stops if the compared
elements differ (i.e., operator==()
returns false) or last1
is
reached. A pair
containing iterators pointing to the final positions is
returned. The second sequence may contain more elements than the first
sequence. The behavior of the algorithm is undefined if the second sequence
contains fewer elements than the first sequence.
first1
and first2
are compared using the binary comparison
operation as defined by comp
, instead of
operator==()
. Comparison stops if the comp
function returns false
or last1
is reached. A pair
containing iterators pointing to the final
positions is returned. The second sequence may contain more elements than the
first sequence. The behavior of the algorithm is undefined if the second
sequence contains fewer elements than the first sequence.
#include <algorithm> #include <string> #include <iostream> #include <utility> class CaseString { public: bool operator()(std::string const &first, std::string const &second) const { return strcasecmp(first.c_str(), second.c_str()) == 0; } }; using namespace std; int main() { string range1[] = { "alpha", "bravo", "foxtrot", "hotel", "zulu" }; string range2[] = { "alpha", "bravo", "foxtrot", "Hotel", "zulu" }; pair<string *, string *> pss = mismatch(range1, range1 + 5, range2); cout << "The elements " << *pss.first << " and " << *pss.second << " at offset " << (pss.first - range1) << " differ\n"; if ( mismatch(range1, range1 + 5, range2, CaseString()).first == range1 + 5 ) cout << "When compared case-insensitively they match\n"; return 0; } /* Generated output: The elements hotel and Hotel at offset 3 differ When compared case-insensitively they match */
#include <algorithm>
bool next_permutation(BidirectionalIterator first,
BidirectionalIterator last);
bool next_permutation(BidirectionalIterator first,
BidirectionalIterator
last, Comp comp);
[first, last)
, is determined. For example, if
the elements 1, 2
and 3
are the range for which next_permutation()
is called, then subsequent calls of next_permutation()
reorders the
following series:
1 2 3 1 3 2 2 1 3 2 3 1 3 1 2 3 2 1This example shows that the elements are reordered such that each new permutation represents the next bigger value (132 is bigger than 123, 213 is bigger than 132, etc.) using
operator<()
of the data type to which the
iterators point. The value
true
is returned if a reordering took place,
the value
false
is returned if no reordering took place, which is the case
if the sequence represents the last (biggest) value. In that case, the
sequence is also sorted using operator<()
.
[first, last)
is determined. The elements in
the range are reordered. The value true
is returned if a reordering took
place, the value false
is returned if no reordering took place, which is
the case if the resulting sequence would haven been ordered using the
binary predicate comp
to compare elements.
#include <algorithm> #include <iterator> #include <iostream> #include <string> class CaseString { public: bool operator()(std::string const &first, std::string const &second) const { return strcasecmp(first.c_str(), second.c_str()) < 0; } }; using namespace std; int main() { string saints[] = {"Oh", "when", "the", "saints"}; cout << "All permutations of 'Oh when the saints':\n"; cout << "Sequences:\n"; do { copy(saints, saints + 4, ostream_iterator<string>(cout, " ")); cout << endl; } while (next_permutation(saints, saints + 4, CaseString())); cout << "After first sorting the sequence:\n"; sort(saints, saints + 4, CaseString()); cout << "Sequences:\n"; do { copy(saints, saints + 4, ostream_iterator<string>(cout, " ")); cout << endl; } while (next_permutation(saints, saints + 4, CaseString())); return 0; } /* Generated output (only partially given): All permutations of 'Oh when the saints': Sequences: Oh when the saints saints Oh the when saints Oh when the saints the Oh when ... After first sorting the sequence: Sequences: Oh saints the when Oh saints when the Oh the saints when Oh the when saints ... */
#include <algorithm>
void nth_element(RandomAccessIterator first,
RandomAccessIterator nth,
RandomAccessIterator
last);
void nth_element(RandomAccessIterator first,
RandomAccessIterator nth,
RandomAccessIterator last, Compare comp);
[first,
last)
are sorted relative to the element pointed to by nth
: all elements
in the range [left, nth)
are smaller than the element pointed to by
nth
, and alle elements in the range [nth + 1, last)
are greater
than the element pointed to by nth
. The two subsets themselves are not
sorted. The operator<()
of the data type to which the iterators point is
used to compare the elements.
[first,
last)
are sorted relative to the element pointed to by nth
: all elements
in the range [left, nth)
are smaller than the element pointed to by
nth
, and alle elements in the range [nth + 1, last)
are greater
than the element pointed to by nth
. The two subsets themselves are not
sorted. The comp
function object is used to compare the elements.
#include <algorithm> #include <iostream> #include <iterator> #include <functional> using namespace std; int main() { int ia[] = {1, 3, 5, 7, 9, 2, 4, 6, 8, 10}; nth_element(ia, ia + 3, ia + 10); cout << "sorting with respect to " << ia[3] << endl; copy(ia, ia + 10, ostream_iterator<int>(cout, " ")); cout << endl; nth_element(ia, ia + 5, ia + 10, greater<int>()); cout << "sorting with respect to " << ia[5] << endl; copy(ia, ia + 10, ostream_iterator<int>(cout, " ")); cout << endl; return 0; } /* Generated output: sorting with respect to 4 1 2 3 4 9 7 5 6 8 10 sorting with respect to 5 10 8 7 9 6 5 3 4 2 1 */
#include <algorithm>
void partial_sort(RandomAccessIterator first,
RandomAccessIterator middle,
RandomAccessIterator last);
void partial_sort(RandomAccessIterator first,
RandomAccessIterator middle,
RandomAccessIterator last, Compare comp);
middle - first
smallest elements
are sorted and stored in the [first, middle)
using the
operator<()
of the data type to which the iterators point. The remaining elements of the
series remain unsorted, and are stored in [middle, last)
.
middle - first
smallest
elements (according to the provided binary predicate comp
) are sorted and
stored in the [first, middle)
. The remaining elements of the series
remain unsorted.
#include <algorithm> #include <iostream> #include <functional> #include <iterator> using namespace std; int main() { int ia[] = {1, 3, 5, 7, 9, 2, 4, 6, 8, 10}; partial_sort(ia, ia + 3, ia + 10); cout << "find the 3 smallest elements:\n"; copy(ia, ia + 10, ostream_iterator<int>(cout, " ")); cout << endl; cout << "find the 5 biggest elements:\n"; partial_sort(ia, ia + 5, ia + 10, greater<int>()); copy(ia, ia + 10, ostream_iterator<int>(cout, " ")); cout << endl; return 0; } /* Generated output: find the 3 smallest elements: 1 2 3 7 9 5 4 6 8 10 find the 5 biggest elements: 10 9 8 7 6 1 2 3 4 5 */
#include <algorithm>
void partial_sort_copy(InputIterator first,
InputIterator last,
RandomAccessIterator dest_first, RandomAccessIterator
dest_last);
void partial_sort_copy(InputIterator first,
InputIterator last,
RandomAccessIterator dest_first, RandomAccessIterator dest_last,
Compare comp);
[first, last)
are copied to the range [dest_first, dest_last)
,
using the
operator<()
of the data type to which the iterators point. Only
the number of elements in the smaller range are copied to the second range.
[first, last)
are are sorted by the binary predicate comp
. The
elements for which the predicate returns most often true
are copied to the
range [dest_first, dest_last)
. Only the number of elements in the
smaller range are copied to the second range.
#include <algorithm> #include <iostream> #include <functional> #include <iterator> using namespace std; int main() { int ia[] = {1, 10, 3, 8, 5, 6, 7, 4, 9, 2}; int ia2[6]; partial_sort_copy(ia, ia + 10, ia2, ia2 + 6); copy(ia, ia + 10, ostream_iterator<int>(cout, " ")); cout << endl; cout << "the 6 smallest elements: "; copy(ia2, ia2 + 6, ostream_iterator<int>(cout, " ")); cout << endl; cout << "the 4 smallest elements to a larger range:\n"; partial_sort_copy(ia, ia + 4, ia2, ia2 + 6); copy(ia2, ia2 + 6, ostream_iterator<int>(cout, " ")); cout << endl; cout << "the 4 biggest elements to a larger range:\n"; partial_sort_copy(ia, ia + 4, ia2, ia2 + 6, greater<int>()); copy(ia2, ia2 + 6, ostream_iterator<int>(cout, " ")); cout << endl; return 0; } /* Generated output: 1 10 3 8 5 6 7 4 9 2 the 6 smallest elements: 1 2 3 4 5 6 the 4 smallest elements to a larger range: 1 3 8 10 5 6 the 4 biggest elements to a larger range: 10 8 3 1 5 6 */
#include <numeric>
OutputIterator partial_sum(InputIterator first,
InputIterator last,
OutputIterator result);
OutputIterator partial_sum(InputIterator first,
InputIterator last,
OutputIterator result, BinaryOperation
op);
[result, <returned OutputIterator>)
receives a value which is obtained
by adding the elements in the corresponding range of the range [first,
last)
. The first element in the resulting range will be equal to the element
pointed to by first
.
[result, <returned OutputIterator>)
is obtained by applying the binary
operator op
to the previous element in the resulting range and the
corresponding element in the range [first, last)
. The first
element in the resulting range will be equal to the element pointed to by
first
.
#include <numeric> #include <algorithm> #include <iostream> #include <functional> #include <iterator> using namespace std; int main() { int ia[] = {1, 2, 3, 4, 5}; int ia2[5]; copy(ia2, partial_sum(ia, ia + 5, ia2), ostream_iterator<int>(cout, " ")); cout << endl; copy(ia2, partial_sum(ia, ia + 5, ia2, multiplies<int>()), ostream_iterator<int>(cout, " ")); cout << endl; return 0; } /* Generated output: 1 3 6 10 15 1 2 6 24 120 */
#include <algorithm>
BidirectionalIterator partition(BidirectionalIterator
first,
BidirectionalIterator last, UnaryPredicate pred);
[first, last)
for which the
unary predicate pred
evaluates as true
are placed before the elements
which evaluate as false
. The return value points just beyond the last
element in the partitioned range for which pred
evaluates as true
.
#include <algorithm> #include <iostream> #include <string> #include <iterator> class LessThan { int d_x; public: LessThan(int x) : d_x(x) {} bool operator()(int value) { return value <= d_x; } }; using namespace std; int main() { int ia[] = {1, 3, 5, 7, 9, 10, 2, 8, 6, 4}; int *split; split = partition(ia, ia + 10, LessThan(ia[9])); cout << "Last element <= 4 is ia[" << split - ia - 1 << "]\n"; copy(ia, ia + 10, ostream_iterator<int>(cout, " ")); cout << endl; return 0; } /* Generated output: Last element <= 4 is ia[3] 1 3 4 2 9 10 7 8 6 5 */
#include <algorithm>
bool prev_permutation(BidirectionalIterator first,
BidirectionalIterator last);
bool prev_permutation(BidirectionalIterator first,
BidirectionalIterator
last, Comp comp);
[first, last)
is determined. The
elements in the range are reordered such that the first ordering is obtained
representing a `smaller' value (see next_permutation()
(section
19.1.32) for an example involving the opposite ordering). The value
true
is returned if a reordering took place, the value false
is
returned if no reordering took place, which is the case if the provided
sequence was already ordered, according to the
operator<()
of the data
type to which the iterators point.
[first, last)
is determined. The
elements in the range are reordered. The value true
is returned if a
reordering took place, the value false
is returned if no reordering took
place, which is the case if the original sequence was already ordered,
using the binary predicate comp
to compare two elements.
#include <algorithm> #include <iostream> #include <string> #include <iterator> class CaseString { public: bool operator()(std::string const &first, std::string const &second) const { return strcasecmp(first.c_str(), second.c_str()) < 0; } }; using namespace std; int main() { string saints[] = {"Oh", "when", "the", "saints"}; cout << "All previous permutations of 'Oh when the saints':\n"; cout << "Sequences:\n"; do { copy(saints, saints + 4, ostream_iterator<string>(cout, " ")); cout << endl; } while (prev_permutation(saints, saints + 4, CaseString())); cout << "After first sorting the sequence:\n"; sort(saints, saints + 4, CaseString()); cout << "Sequences:\n"; while (prev_permutation(saints, saints + 4, CaseString())) { copy(saints, saints + 4, ostream_iterator<string>(cout, " ")); cout << endl; } cout << "No (more) previous permutations\n"; return 0; } /* Generated output: All previous permutations of 'Oh when the saints': Sequences: Oh when the saints Oh when saints the Oh the when saints Oh the saints when Oh saints when the Oh saints the when After first sorting the sequence: Sequences: No (more) previous permutations */
#include <algorithm>
void random_shuffle(RandomAccessIterator first,
RandomAccessIterator last);
void random_shuffle(RandomAccessIterator first,
RandomAccessIterator last,
RandomNumberGenerator rand);
[first,
last)
are randomly reordered.
[first, last)
are randomly reordered using the rand
random number generator, which should return an int
in the range
[0, remaining)
, where remaining
is passed as argument to the
operator()()
of the rand
function object. Alternatively, the random
number generator may be a function expecting an int remaining
parameter
and returning an int
randomvalue in the range [0, remaining)
. Note
that when a function object is used, it cannot be an anonymous object. The
function in the example uses a procedure outlined in Press et al. (1992)
Numerical Recipes in C: The
Art of Scientific Computing (New York: Cambridge University Press, (2nd ed.,
p. 277)).
#include <algorithm> #include <iostream> #include <string> #include <time.h> #include <iterator> int randomValue(int remaining) { return static_cast<int> ( ((0.0 + remaining) * rand()) / (RAND_MAX + 1.0) ); } class RandomGenerator { public: RandomGenerator() { srand(time(0)); } int operator()(int remaining) const { return randomValue(remaining); } }; void show(std::string *begin, std::string *end) { std::copy(begin, end, std::ostream_iterator<std::string>(std::cout, " ")); std::cout << std::endl << std::endl; } using namespace std; int main() { string words[] = { "kilo", "lima", "mike", "november", "oscar", "papa"}; size_t const size = sizeof(words) / sizeof(string); cout << "Using Default Shuffle:\n"; random_shuffle(words, words + size); show(words, words + size); cout << "Using RandomGenerator:\n"; RandomGenerator rg; random_shuffle(words, words + size, rg); show(words, words + size); srand(time(0) << 1); cout << "Using the randomValue() function:\n"; random_shuffle(words, words + size, randomValue); show(words, words + size); return 0; } /* Generated output (for example): Using Default Shuffle: lima oscar mike november papa kilo Using RandomGenerator: kilo lima papa oscar mike november Using the randomValue() function: mike papa november kilo oscar lima */
#include <algorithm>
ForwardIterator remove(ForwardIterator first,
ForwardIterator last,
Type const &value);
[first, last)
are reordered in such a way that all values unequal to value
are placed at
the beginning of the range. The returned forward iterator points to the first
element that can be removed after reordering. The range [returnvalue,
last)
is called the
leftover of the algorithm. Note that the leftover may
contain elements different from value
, but these elements can be removed
safely, as such elements will also be present in the range [first,
return value)
. Such duplication is the result of the fact that the algorithm
copies, rather than moves elements into new locations. The function
uses operator==()
of the data type to which the iterators point to
determine which elements to remove.
#include <algorithm> #include <iostream> #include <string> #include <iterator> using namespace std; int main() { string words[] = { "kilo", "alpha", "lima", "mike", "alpha", "november", "alpha", "alpha", "alpha", "papa", "quebec" }; string *removed; size_t const size = sizeof(words) / sizeof(string); cout << "Removing all \"alpha\"s:\n"; removed = remove(words, words + size, "alpha"); copy(words, removed, ostream_iterator<string>(cout, " ")); cout << endl << "Leftover elements are:\n"; copy(removed, words + size, ostream_iterator<string>(cout, " ")); cout << endl; return 0; } /* Generated output: Removing all "alpha"s: kilo lima mike november oscar papa quebec Trailing elements are: oscar alpha alpha papa quebec */
#include <algorithm>
OutputIterator remove_copy(InputIterator first,
InputIterator last,
OutputIterator result, Type const &value);
[first, last)
not matching value
are copied to the range [result, returnvalue)
,
where returnvalue
is the value returned by the function. The range
[first, last)
is not modified. The function uses operator==()
of
the data type to which the iterators point to determine which elements not to
copy.
#include <algorithm> #include <iostream> #include <string> #include <functional> #include <iterator> using namespace std; int main() { string words[] = { "kilo", "alpha", "lima", "mike", "alpha", "november", "alpha", "oscar", "alpha", "alpha", "papa", "quebec" }; size_t const size = sizeof(words) / sizeof(string); string remaining [ size - count_if ( words, words + size, bind2nd(equal_to<string>(), string("alpha")) ) ]; string *returnvalue = remove_copy(words, words + size, remaining, "alpha"); cout << "Removing all \"alpha\"s:\n"; copy(remaining, returnvalue, ostream_iterator<string>(cout, " ")); cout << endl; return 0; } /* Generated output: Removing all "alpha"s: kilo lima mike november oscar papa quebec */
#include <algorithm>
OutputIterator remove_copy_if(InputIterator first,
InputIterator last,
OutputIterator result, UnaryPredicate pred);
[first, last)
for which the unary predicate pred
returns true
are copied to the
range [result, returnvalue)
, where returnvalue
is the value
returned by the function. The range [first, last)
is not modified.
#include <algorithm> #include <iostream> #include <string> #include <functional> #include <iterator> using namespace std; int main() { string words[] = { "kilo", "alpha", "lima", "mike", "alpha", "november", "alpha", "oscar", "alpha", "alpha", "papa", "quebec" }; size_t const size = sizeof(words) / sizeof(string); string remaining[ size - count_if ( words, words + size, bind2nd(equal_to<string>(), "alpha") ) ]; string *returnvalue = remove_copy_if ( words, words + size, remaining, bind2nd(equal_to<string>(), "alpha") ); cout << "Removing all \"alpha\"s:\n"; copy(remaining, returnvalue, ostream_iterator<string>(cout, " ")); cout << endl; return 0; } /* Generated output: Removing all "alpha"s: kilo lima mike november oscar papa quebec */
#include <algorithm>
ForwardIterator remove_if(ForwardIterator first,
ForwardIterator last,
UnaryPredicate pred);
[first, last)
are reordered in such a way that all values for which the unary predicate
pred
evaluates as false
are placed at the beginning of the range. The
returned forward iterator points to the first element, after reordering, for
which pred
returns true
. The range [returnvalue, last)
is
called the leftover of the algorithm. The leftover may contain elements
for which the predicate pred
returns false
, but these can safely
be removed, as such elements will also be present in the range [first,
returnvalue)
. Such duplication is the result of the fact that the algorithm
copies, rather than moves elements into new locations.
#include <functional> #include <algorithm> #include <iostream> #include <string> #include <iterator> using namespace std; int main() { string words[] = { "kilo", "alpha", "lima", "mike", "alpha", "november", "alpha", "oscar", "alpha", "alpha", "papa", "quebec" }; size_t const size = sizeof(words) / sizeof(string); cout << "Removing all \"alpha\"s:\n"; string *removed = remove_if(words, words + size, bind2nd(equal_to<string>(), string("alpha"))); copy(words, removed, ostream_iterator<string>(cout, " ")); cout << endl << "Trailing elements are:\n"; copy(removed, words + size, ostream_iterator<string>(cout, " ")); cout << endl; return 0; } /* Generated output: Removing all "alpha"s: kilo lima mike november oscar papa quebec Trailing elements are: oscar alpha alpha papa quebec */
#include <algorithm>
ForwardIterator replace(ForwardIterator first,
ForwardIterator last,
Type const &oldvalue, Type const &newvalue);
oldvalue
in the range pointed to by
[first, last)
are replaced by a copy of newvalue
. The algorithm
uses operator==()
of the data type to which the iterators point.
#include <algorithm> #include <iostream> #include <string> #include <iterator> using namespace std; int main() { string words[] = { "kilo", "alpha", "lima", "mike", "alpha", "november", "alpha", "oscar", "alpha", "alpha", "papa", "quebec" }; size_t const size = sizeof(words) / sizeof(string); replace(words, words + size, string("alpha"), string("ALPHA")); copy(words, words + size, ostream_iterator<string>(cout, " ")); cout << endl; return 0; } /* Generated output: kilo ALPHA lima mike ALPHA november ALPHA oscar ALPHA ALPHA papa quebec */
#include <algorithm>
OutputIterator replace_copy(InputIterator first,
InputIterator last,
OutputIterator result, Type const &oldvalue,
Type const &newvalue);
oldvalue
in the range pointed to by
[first, last)
are replaced by a copy of newvalue
in a new range
[result, returnvalue)
, where returnvalue
is the return value of the
function. The algorithm uses operator==()
of the data type to which the
iterators point.
#include <algorithm> #include <iostream> #include <string> #include <iterator> using namespace std; int main() { string words[] = { "kilo", "alpha", "lima", "mike", "alpha", "november", "alpha", "oscar", "alpha", "alpha", "papa", "quebec" }; size_t const size = sizeof(words) / sizeof(string); string remaining[size]; copy ( remaining, replace_copy(words, words + size, remaining, string("alpha"), string("ALPHA")), ostream_iterator<string>(cout, " ") ); cout << endl; return 0; } /* Generated output: kilo ALPHA lima mike ALPHA november ALPHA oscar ALPHA ALPHA papa quebec */
#include <algorithm>
OutputIterator replace_copy_if(ForwardIterator first,
ForwardIterator
last, OutputIterator result, UnaryPredicate
pred, Type const &value);
[first, last)
are copied to the range [result, returnvalue)
, where returnvalue
is
the value returned by the function. The elements for which the unary predicate
pred
returns true
are replaced by newvalue
. The range
[first, last)
is not modified.
#include <algorithm> #include <iostream> #include <string> #include <functional> #include <iterator> using namespace std; int main() { string words[] = { "kilo", "alpha", "lima", "mike", "alpha", "november", "alpha", "oscar", "alpha", "alpha", "papa", "quebec" }; size_t const size = sizeof(words) / sizeof(string); string result[size]; replace_copy_if(words, words + size, result, bind1st(greater<string>(), string("mike")), string("ALPHA")); copy (result, result + size, ostream_iterator<string>(cout, " ")); cout << endl; return 0; } /* Generated output (all on one line): ALPHA ALPHA ALPHA mike ALPHA november ALPHA oscar ALPHA ALPHA papa quebec */
#include <algorithm>
ForwardIterator replace_if(ForwardIterator first,
ForwardIterator last,
UnaryPredicate pred, Type const &value);
[first, last)
for which the unary predicate pred
evaluates as true
are replaced by newvalue
.
Example:#include <algorithm> #include <iostream> #include <string> #include <functional> #include <iterator> using namespace std; int main() { string words[] = { "kilo", "alpha", "lima", "mike", "alpha", "november", "alpha", "oscar", "alpha", "alpha", "papa", "quebec" }; size_t const size = sizeof(words) / sizeof(string); replace_if(words, words + size, bind1st(equal_to<string>(), string("alpha")), string("ALPHA")); copy(words, words + size, ostream_iterator<string>(cout, " ")); cout << endl; return 0; } /* generated output: kilo ALPHA lima mike ALPHA november ALPHA oscar ALPHA ALPHA papa quebec */
#include <algorithm>
void reverse(BidirectionalIterator first,
BidirectionalIterator last);
[first, last)
are reversed.
#include <algorithm> #include <iostream> #include <string> using namespace std; int main() { string line; while (getline(cin, line)) { reverse(line.begin(), line.end()); cout << line << endl; } return 0; }
#include <algorithm>
OutputIterator reverse_copy(BidirectionalIterator first,
BidirectionalIterator last, OutputIterator result);
[first, last)
are copied to the range [result, returnvalue)
in reversed order. The
value returnvalue
is the value that is returned by the function.
#include <algorithm> #include <iostream> #include <string> using namespace std; int main() { string line; while (getline(cin, line)) { size_t size = line.size(); char copy[size + 1]; cout << "line: " << line << endl << "reversed: "; reverse_copy(line.begin(), line.end(), copy); copy[size] = 0; // 0 is not part of the reversed // line ! cout << copy << endl; } return 0; }
#include <algorithm>
void rotate(ForwardIterator first, ForwardIterator
middle, ForwardIterator
last);
[first, middle)
are
moved to the end of the container, the elements implied by the range
[middle, last)
are moved to the beginning of the container, keeping the
order of the elements in the two subsets intact.
#include <algorithm> #include <iostream> #include <string> #include <iterator> using namespace std; int main() { string words[] = { "kilo", "lima", "mike", "november", "oscar", "papa", "echo", "foxtrot", "golf", "hotel", "india", "juliet" }; size_t const size = sizeof(words) / sizeof(string); size_t const midsize = 6; rotate(words, words + midsize, words + size); copy(words, words + size, ostream_iterator<string>(cout, " ")); cout << endl; return 0; } /* Generated output: echo foxtrot golf hotel india juliet kilo lima mike november oscar papa */
#include <algorithm>
OutputIterator rotate_copy(ForwardIterator first,
ForwardIterator middle,
ForwardIterator last, OutputIterator result);
[middle, last)
and
then the elements implied by the range [first, middle)
are copied to the
destination container having range [result, returnvalue)
, where
returnvalue
is the iterator returned by the function. The original order
of the elements in the two subsets is not altered.
#include <algorithm> #include <iostream> #include <string> #include <iterator> using namespace std; int main() { string words[] = { "kilo", "lima", "mike", "november", "oscar", "papa", "echo", "foxtrot", "golf", "hotel", "india", "juliet" }; size_t const size = sizeof(words) / sizeof(string); size_t midsize = 6; string out[size]; copy(out, rotate_copy(words, words + midsize, words + size, out), ostream_iterator<string>(cout, " ")); cout << endl; return 0; } /* Generated output: echo foxtrot golf hotel india juliet kilo lima mike november oscar papa */
#include <algorithm>
ForwardIterator1 search(ForwardIterator1 first1,
ForwardIterator1 last1,
ForwardIterator2 first2, ForwardIterator2 last2);
ForwardIterator1 search(ForwardIterator1 first1,
ForwardIterator1 last1,
ForwardIterator2 first2, ForwardIterator2 last2,
BinaryPredicate pred);
[first1, last1)
is returned where the elements in the range
[first2, last2)
are found using
operator==()
operator of the data
type to which the iterators point. If no such location exists, last1
is
returned.
[first1, last1)
is returned where the elements in the range
[first2, last2)
are found using the provided binary predicate pred
to compare the elements in the two ranges. If no such location exists,
last1
is returned.
#include <algorithm> #include <iostream> #include <iterator> class absInt { public: bool operator()(int i1, int i2) { return abs(i1) == abs(i2); } }; using namespace std; int main() { int range1[] = {-2, -4, -6, -8, 2, 4, 6, 8}; int range2[] = {6, 8}; copy ( search(range1, range1 + 8, range2, range2 + 2), range1 + 8, ostream_iterator<int>(cout, " ") ); cout << endl; copy ( search(range1, range1 + 8, range2, range2 + 2, absInt()), range1 + 8, ostream_iterator<int>(cout, " ") ); cout << endl; return 0; } /* Generated output: 6 8 -6 -8 2 4 6 8 */
#include <algorithm>
ForwardIterator1 search_n(ForwardIterator1 first1,
ForwardIterator1 last1, Size count, Type const &value);
ForwardIterator1 search_n(ForwardIterator1 first1,
ForwardIterator1 last1, Size count, Type const &value, BinaryPredicate
pred);
[first1, last1)
is returned where n
consecutive elements having
value value
are found using
operator==()
of the data type to which
the iterators point to compare the elements. If no such location exists,
last1
is returned.
[first1, last1)
is returned where n
consecutive elements having
value value
are found using the provided binary predicate pred
to
compare the elements. If no such location exists, last1
is returned.
#include <algorithm> #include <iostream> #include <iterator> class absInt { public: bool operator()(int i1, int i2) { return abs(i1) == abs(i2); } }; using namespace std; int main() { int range1[] = {-2, -4, -4, -6, -8, 2, 4, 4, 6, 8}; int range2[] = {6, 8}; copy ( search_n(range1, range1 + 8, 2, 4), range1 + 8, ostream_iterator<int>(cout, " ") ); cout << endl; copy ( search_n(range1, range1 + 8, 2, 4, absInt()), range1 + 8, ostream_iterator<int>(cout, " ") ); cout << endl; return 0; } /* Generated output: 4 4 -4 -4 -6 -8 2 4 4 */
#include <algorithm>
OutputIterator set_difference(InputIterator1
first1, InputIterator1 last1,
InputIterator2 first2, InputIterator2 last2,
OutputIterator result);
OutputIterator set_difference(InputIterator1
first1, InputIterator1 last1,
InputIterator2 first2, InputIterator2 last2,
OutputIterator result,
Compare comp);
[first1, last1)
that are not present in the
range [first2, last2)
is returned, starting at result
, and ending
at the OutputIterator
returned by the function. The elements in the two
ranges must have been sorted using
operator<()
of the data type to which
the iterators point.
[first1, last1)
that are not present in the
range [first2, last2)
is returned, starting at result
, and ending
at the OutputIterator
returned by the function. The elements in the two
ranges must have been sorted using the comp
function object.
#include <algorithm> #include <iostream> #include <string> #include <iterator> class CaseLess { public: bool operator()(std::string const &left, std::string const &right) { return strcasecmp(left.c_str(), right.c_str()) < 0; } }; using namespace std; int main() { string set1[] = { "kilo", "lima", "mike", "november", "oscar", "papa", "quebec" }; string set2[] = { "papa", "quebec", "romeo"}; string result[7]; string *returned; copy(result, set_difference(set1, set1 + 7, set2, set2 + 3, result), ostream_iterator<string>(cout, " ")); cout << endl; string set3[] = { "PAPA", "QUEBEC", "ROMEO"}; copy(result, set_difference(set1, set1 + 7, set3, set3 + 3, result, CaseLess()), ostream_iterator<string>(cout, " ")); cout << endl; return 0; } /* Generated output: kilo lima mike november oscar kilo lima mike november oscar */
#include <algorithm>
OutputIterator set_intersection(InputIterator1 first1,
InputIterator1
last1, InputIterator2 first2, InputIterator2
last2, OutputIterator
result);
OutputIterator set_intersection(InputIterator1 first1,
InputIterator1
last1, InputIterator2 first2, InputIterator2
last2, OutputIterator
result, Compare comp);
[first1, last1)
that are also present in the
range [first2, last2)
is returned, starting at result
, and ending
at the OutputIterator
returned by the function. The elements in the two
ranges must have been sorted using
operator<()
of the data type to which
the iterators point.
[first1, last1)
that are also present in the
range [first2, last2)
is returned, starting at result
, and ending
at the OutputIterator
returned by the function. The elements in the two
ranges must have been sorted using the comp
function object.
#include <algorithm> #include <iostream> #include <string> #include <iterator> class CaseLess { public: bool operator()(std::string const &left, std::string const &right) { return strcasecmp(left.c_str(), right.c_str()) < 0; } }; using namespace std; int main() { string set1[] = { "kilo", "lima", "mike", "november", "oscar", "papa", "quebec" }; string set2[] = { "papa", "quebec", "romeo"}; string result[7]; string *returned; copy(result, set_intersection(set1, set1 + 7, set2, set2 + 3, result), ostream_iterator<string>(cout, " ")); cout << endl; string set3[] = { "PAPA", "QUEBEC", "ROMEO"}; copy(result, set_intersection(set1, set1 + 7, set3, set3 + 3, result, CaseLess()), ostream_iterator<string>(cout, " ")); cout << endl; return 0; } /* Generated output: papa quebec papa quebec */
#include <algorithm>
OutputIterator set_symmetric_difference(
InputIterator1 first1,
InputIterator1 last1, InputIterator2 first2,
InputIterator2 last2, OutputIterator result);
OutputIterator set_symmetric_difference(
InputIterator1 first1,
InputIterator1 last1, InputIterator2 first2,
InputIterator2 last2, OutputIterator result,
Compare comp);
[first1, last1)
that are not present in the
range [first2, last2)
and those in the range [first2, last2)
that are not present in the range [first1, last1)
is returned, starting
at result
, and ending at the OutputIterator
returned by the
function. The elements in the two ranges must have been sorted using
operator<()
of the data type to which the iterators point.
[first1, last1)
that are not present in the
range [first2, last2)
and those in the range [first2, last2)
that are not present in the range [first1, last1)
is returned, starting
at result
, and ending at the OutputIterator
returned by the
function. The elements in the two ranges must have been sorted using the
comp
function object.
#include <algorithm> #include <iostream> #include <string> #include <iterator> class CaseLess { public: bool operator()(std::string const &left, std::string const &right) { return strcasecmp(left.c_str(), right.c_str()) < 0; } }; using namespace std; int main() { string set1[] = { "kilo", "lima", "mike", "november", "oscar", "papa", "quebec" }; string set2[] = { "papa", "quebec", "romeo"}; string result[7]; string *returned; copy(result, set_symmetric_difference(set1, set1 + 7, set2, set2 + 3, result), ostream_iterator<string>(cout, " ")); cout << endl; string set3[] = { "PAPA", "QUEBEC", "ROMEO"}; copy(result, set_symmetric_difference(set1, set1 + 7, set3, set3 + 3, result, CaseLess()), ostream_iterator<string>(cout, " ")); cout << endl; return 0; } /* Generated output: kilo lima mike november oscar romeo kilo lima mike november oscar ROMEO */
#include <algorithm>
OutputIterator set_union(InputIterator1 first1,
InputIterator1 last1,
InputIterator2 first2, InputIterator2 last2,
OutputIterator result);
OutputIterator set_union(InputIterator1 first1,
InputIterator1 last1,
InputIterator2 first2, InputIterator2 last2,
OutputIterator result,
Compare comp);
[first1, last1)
or the range
[first2, last2)
or in both ranges is returned, starting at result
,
and ending at the OutputIterator
returned by the function. The elements in
the two ranges must have been sorted using
operator<()
of the data type to
which the iterators point. Note that in the final range each element will
appear only once.
[first1, last1)
or the range
[first2, last2)
or in both ranges is returned, starting at result
,
and ending at the OutputIterator
returned by the function. The elements in
the two ranges must have been sorted using comp
function object. Note that
in the final range each element will appear only once.
#include <algorithm> #include <iostream> #include <string> #include <iterator> class CaseLess { public: bool operator()(std::string const &left, std::string const &right) { return strcasecmp(left.c_str(), right.c_str()) < 0; } }; using namespace std; int main() { string set1[] = { "kilo", "lima", "mike", "november", "oscar", "papa", "quebec" }; string set2[] = { "papa", "quebec", "romeo"}; string result[7]; string *returned; copy(result, set_union(set1, set1 + 7, set2, set2 + 3, result), ostream_iterator<string>(cout, " ")); cout << endl; string set3[] = { "PAPA", "QUEBEC", "ROMEO"}; copy(result, set_union(set1, set1 + 7, set3, set3 + 3, result, CaseLess()), ostream_iterator<string>(cout, " ")); cout << endl; return 0; } /* Generated output: kilo lima mike november oscar papa quebec romeo kilo lima mike november oscar papa quebec ROMEO */
#include <algorithm>
void sort(RandomAccessIterator first,
RandomAccessIterator last);
void sort(RandomAccessIterator first,
RandomAccessIterator last,
Compare comp);
[first,
last)
are sorted in ascending order using
operator<()
of the data type to
which the iterators point.
[first, last)
are sorted in ascending order using the comp
function object to compare the elements. The binary predicate comp
should return true
if its first argument should be placed earlier in the
sorted sequence than its second argument.
#include <algorithm> #include <iostream> #include <string> #include <functional> #include <iterator> using namespace std; int main() { string words[] = {"november", "kilo", "mike", "lima", "oscar", "quebec", "papa"}; sort(words, words + 7); copy(words, words + 7, ostream_iterator<string>(cout, " ")); cout << endl; sort(words, words + 7, greater<string>()); copy(words, words + 7, ostream_iterator<string>(cout, " ")); cout << endl; return 0; } /* Generated output: kilo lima mike november oscar papa quebec quebec papa oscar november mike lima kilo */
#include <algorithm>
BidirectionalIterator
stable_partition(BidirectionalIterator first,
BidirectionalIterator last, UnaryPredicate pred);
[first, last)
for which the
unary predicate pred
evaluates as true
are placed before the elements
which evaluate as false
. Apart from this reordering, the relative order of
all elements for which the predicate evaluates to false
and the relative
order of all elements for which the predicate evaluates to true
is kept.
The return value points just beyond the last element in the
partitioned range for which pred
evaluates as true
.
#include <algorithm> #include <iostream> #include <string> #include <functional> #include <iterator> using namespace std; int main() { int org[] = {1, 3, 5, 7, 9, 10, 2, 8, 6, 4}; int ia[10]; int *split; copy(org, org + 10, ia); split = partition(ia, ia + 10, bind2nd(less_equal<int>(), ia[9])); cout << "Last element <= 4 is ia[" << split - ia - 1 << "]\n"; copy(ia, ia + 10, ostream_iterator<int>(cout, " ")); cout << endl; copy(org, org + 10, ia); split = stable_partition(ia, ia + 10, bind2nd(less_equal<int>(), ia[9])); cout << "Last element <= 4 is ia[" << split - ia - 1 << "]\n"; copy(ia, ia + 10, ostream_iterator<int>(cout, " ")); cout << endl; return 0; } /* Generated output: Last element <= 4 is ia[3] 1 3 4 2 9 10 7 8 6 5 Last element <= 4 is ia[3] 1 3 2 4 5 7 9 10 8 6 */
#include <algorithm>
void stable_sort(RandomAccessIterator first,
RandomAccessIterator last);
void stable_sort(RandomAccessIterator first,
RandomAccessIterator last,
Compare comp);
[first,
last)
are stable-sorted in ascending order using
operator<()
of the data
type to which the iterators point: the relative order of equal elements is
kept.
[first, last)
are stable-sorted in ascending order using the comp
binary predicate to compare the elements. This predicate should return
true
if its first argument should be placed before its second argument in
the sorted set of element.
#include <algorithm> #include <iostream> #include <string> #include <vector> #include <iterator> typedef std::pair<std::string, std::string> pss; // 1 (see the text) namespace std { ostream &operator<<(ostream &out, pss const &p) // 2 { return out << " " << p.first << " " << p.second << endl; } } class sortby { std::string pss::*d_field; public: sortby(std::string pss::*field) // 3 : d_field(field) {} bool operator()(pss const &p1, pss const &p2) const // 4 { return p1.*d_field < p2.*d_field; } }; using namespace std; int main() { vector<pss> namecity; // 5 namecity.push_back(pss("Hampson", "Godalming")); namecity.push_back(pss("Moran", "Eugene")); namecity.push_back(pss("Goldberg", "Eugene")); namecity.push_back(pss("Moran", "Godalming")); namecity.push_back(pss("Goldberg", "Chicago")); namecity.push_back(pss("Hampson", "Eugene")); sort(namecity.begin(), namecity.end(), sortby(&pss::first)); // 6 cout << "sorted by names:\n"; copy(namecity.begin(), namecity.end(), ostream_iterator<pss>(cout)); // 7 stable_sort(namecity.begin(), namecity.end(), sortby(&pss::second)); cout << "sorted by names within sorted cities:\n"; copy(namecity.begin(), namecity.end(), ostream_iterator<pss>(cout)); return 0; } /* Generated output: sorted by names: Goldberg Eugene Goldberg Chicago Hampson Godalming Hampson Eugene Moran Eugene Moran Godalming sorted by names within sorted cities: Goldberg Chicago Goldberg Eugene Hampson Eugene Moran Eugene Hampson Godalming Moran Godalming */
typedef
is used to reduce the clutter that occurs from
the repeated use of pair<string, string>
.
operator
<< is overloaded to be able to insert
a pair
into an
ostream
object. This is merely a service function to
make life easy. Note, however, that this function is put in the std
namespace. If this namespace wrapping is omitted, it won't be used, as
ostream
's operator
<< operators must be part of the std
namespace.
sortby
is defined, allowing us to construct an
anonymous object which receives a pointer to one of the pair
data
members that are used for sorting. In this case, as both members are
string
objects, the constructor can easily be defined: its parameter is a
pointer to a string
member of the class pair<string, string>
.
operator()()
member will receive two pair
references,
and it will then use the pointer to its members, stored in the sortby
object, to compare the appropriate fields of the pairs
.
main()
, first some data is stored in a vector
.
sort()
will suffice. Since we
want the names to be sorted within cities, the names represent the least
important criterion, so we sort by names: sortby(&pss::first)
.
stable_sort()
, the ties that are observed when cities are sorted are
solved in such a way that the existing relative ordering will not be
broken. So, we end up getting Goldberg in Eugene before Hampson in Eugene,
before Moran in Eugene. To sort by cities, we use another anonymous sortby
object: sortby(&pss::second)
.
#include <algorithm>
void swap(Type &object1, Type &object2);
object1
and object2
exchange their values.
#include <algorithm> #include <iostream> #include <string> #include <iterator> using namespace std; int main() { string first[] = {"alpha", "bravo", "charley"}; string second[] = {"echo", "foxtrot", "golf"}; size_t const n = sizeof(first) / sizeof(string); cout << "Before:\n"; copy(first, first + n, ostream_iterator<string>(cout, " ")); cout << endl; copy(second, second + n, ostream_iterator<string>(cout, " ")); cout << endl; for (size_t idx = 0; idx < n; ++idx) swap(first[idx], second[idx]); cout << "After:\n"; copy(first, first + n, ostream_iterator<string>(cout, " ")); cout << endl; copy(second, second + n, ostream_iterator<string>(cout, " ")); cout << endl; return 0; } /* Generated output: Before: alpha bravo charley echo foxtrot golf After: echo foxtrot golf alpha bravo charley */
#include <algorithm>
ForwardIterator2 swap_ranges(ForwardIterator1 first1,
ForwardIterator1
last1, ForwardIterator2 result);
[first1, last1)
are swapped with the elements in the
range [result, returnvalue)
, where returnvalue
is the value
returned by the function. The two ranges must be disjoint.
#include <algorithm> #include <iostream> #include <string> #include <iterator> using namespace std; int main() { string first[] = {"alpha", "bravo", "charley"}; string second[] = {"echo", "foxtrot", "golf"}; size_t const n = sizeof(first) / sizeof(string); cout << "Before:\n"; copy(first, first + n, ostream_iterator<string>(cout, " ")); cout << endl; copy(second, second + n, ostream_iterator<string>(cout, " ")); cout << endl; swap_ranges(first, first + n, second); cout << "After:\n"; copy(first, first + n, ostream_iterator<string>(cout, " ")); cout << endl; copy(second, second + n, ostream_iterator<string>(cout, " ")); cout << endl; return 0; } /* Generated output: Before: alpha bravo charley echo foxtrot golf After: echo foxtrot golf alpha bravo charley */
#include <algorithm>
OutputIterator transform(InputIterator first,
InputIterator last,
OutputIterator result, UnaryOperator op);
OutputIterator transform(InputIterator1 first1,
InputIterator1 last1,
InputIterator2 first2, OutputIterator result,
BinaryOperator op);
op
is applied to
each of the elements in the range [first, last)
, and the resulting
values are stored in the range starting at result
. The return value points
just beyond the last generated element.
op
is applied
to each of the elements in the range [first1, last1)
and the
corresponding element in the second range starting at first2
. The
resulting values are stored in the range starting at result
. The return
value points just beyond the last generated element.
#include <functional> #include <vector> #include <algorithm> #include <iostream> #include <string> #include <cctype> #include <iterator> class Caps { public: std::string operator()(std::string const &src) { std::string tmp = src; transform(tmp.begin(), tmp.end(), tmp.begin(), toupper); return tmp; } }; using namespace std; int main() { string words[] = {"alpha", "bravo", "charley"}; copy(words, transform(words, words + 3, words, Caps()), ostream_iterator<string>(cout, " ")); cout << endl; int values[] = {1, 2, 3, 4, 5}; vector<int> squares; transform(values, values + 5, values, back_inserter(squares), multiplies<int>()); copy(squares.begin(), squares.end(), ostream_iterator<int>(cout, " ")); cout << endl; return 0; } /* Generated output: ALPHA BRAVO CHARLEY 1 4 9 16 25 */
for_each()
(section
19.1.17) and transform()
generic algorithms should be noted:
transform()
the return value of the function
object's operator()()
member is used; the argument that is passed to the
operator()()
member itself is not changed.
for_each()
the function object's operator()()
receives a reference to an argument, which itself may be changed by the
function object's operator()()
.
#include <algorithm>
ForwardIterator unique(ForwardIterator first,
ForwardIterator last);
ForwardIterator unique(ForwardIterator first,
ForwardIterator last,
BinaryPredicate pred);
operator==()
, all but the
first of consecutively equal elements of the data type to which the iterators
point in the range pointed to by [first, last)
are relocated to the
end of the range. The returned forward iterator marks the beginning of the
leftover. All elements in the range [first, return-value)
are
unique, all elements in the range [return-value, last)
are equal to
elements in the range [first, return-value)
.
[first, last)
for which the binary
predicate pred
(expecting two arguments of the data type to which the
iterators point) returns true
, are relocated to the end of the range. The
returned forward iterator marks the beginning of the
leftover. For all
pairs of elements in the range [first, return-value)
pred
returns
false
(i.e., are unique), while pred
returns true
for a
combination of, as its first operand, an element in the range
[return-value, last)
and, as its second operand, an element in the
range [first, return-value)
.
#include <algorithm> #include <iostream> #include <string> #include <iterator> class CaseString { public: bool operator()(std::string const &first, std::string const &second) const { return !strcasecmp(first.c_str(), second.c_str()); } }; using namespace std; int main() { string words[] = {"alpha", "alpha", "Alpha", "papa", "quebec" }; size_t const size = sizeof(words) / sizeof(string); string *removed = unique(words, words + size); copy(words, removed, ostream_iterator<string>(cout, " ")); cout << endl << "Trailing elements are:\n"; copy(removed, words + size, ostream_iterator<string>(cout, " ")); cout << endl; removed = unique(words, words + size, CaseString()); copy(words, removed, ostream_iterator<string>(cout, " ")); cout << endl << "Trailing elements are:\n"; copy(removed, words + size, ostream_iterator<string>(cout, " ")); cout << endl; return 0; } /* Generated output: alpha Alpha papa quebec Trailing elements are: quebec alpha papa quebec Trailing elements are: quebec quebec */
#include <algorithm>
OutputIterator unique_copy(InputIterator first,
InputIterator last,
OutputIterator result);
OutputIterator unique_copy(InputIterator first,
InputIterator last,
OutputIterator Result, BinaryPredicate
pred);
[first,
last)
are copied to the resulting container, starting at result
.
Consecutively equal elements (using
operator==()
of the data type to which
the iterators point) are copied only once. The returned output iterator points
just beyond the last copied element.
[first,
last)
are copied to the resulting container, starting at result
.
Consecutive elements in the range pointed to by [first, last)
for which
the binary predicate pred
returns true
are copied only once. The
returned output iterator points just beyond the last copied element.
#include <algorithm> #include <iostream> #include <string> #include <vector> #include <iterator> class CaseString { public: bool operator()(std::string const &first, std::string const &second) const { return !strcasecmp(first.c_str(), second.c_str()); } }; using namespace std; int main() { string words[] = {"oscar", "Alpha", "alpha", "alpha", "papa", "quebec" }; size_t const size = sizeof(words) / sizeof(string); vector<string> remaining; unique_copy(words, words + size, back_inserter(remaining)); copy(remaining.begin(), remaining.end(), ostream_iterator<string>(cout, " ")); cout << endl; vector<string> remaining2; unique_copy(words, words + size, back_inserter(remaining2), CaseString()); copy(remaining2.begin(), remaining2.end(), ostream_iterator<string>(cout, " ")); cout << endl; return 0; } /* Generated output: oscar Alpha alpha papa quebec oscar Alpha papa quebec */
#include <algorithm>
ForwardIterator upper_bound(ForwardIterator first,
ForwardIterator last,
Type const &value);
ForwardIterator upper_bound(ForwardIterator first,
ForwardIterator last,
Type const &value, Compare comp);
[first, last)
are searched for the first element that is
greater than value
. The returned iterator marks the first location in the
sequence where value
can be inserted without breaking the sorted order of
the elements using
operator<()
of the data type to which the iterators
point. If no such element is found, last
is returned.
[first, last)
must have been sorted using the comp
function
or function object. Each element in the range is compared to value
using
the comp
function. An iterator to the first element for which the binary
predicate comp
, applied to the elements of the range and value
,
returns true
is returned. If no such element is found, last
is
returned.
#include <algorithm> #include <iostream> #include <functional> #include <iterator> using namespace std; int main() { int ia[] = {10, 15, 15, 20, 30}; size_t n = sizeof(ia) / sizeof(int); cout << "Sequence: "; copy(ia, ia + n, ostream_iterator<int>(cout, " ")); cout << endl; cout << "15 can be inserted before " << *upper_bound(ia, ia + n, 15) << endl; cout << "35 can be inserted after " << (upper_bound(ia, ia + n, 35) == ia + n ? "the last element" : "???") << endl; sort(ia, ia + n, greater<int>()); cout << "Sequence: "; copy(ia, ia + n, ostream_iterator<int>(cout, " ")); cout << endl; cout << "15 can be inserted before " << *upper_bound(ia, ia + n, 15, greater<int>()) << endl; cout << "35 can be inserted before " << (upper_bound(ia, ia + n, 35, greater<int>()) == ia ? "the first element " : "???") << endl; return 0; } /* Generated output: Sequence: 10 15 15 20 30 15 can be inserted before 20 35 can be inserted after the last element Sequence: 30 20 15 15 10 15 can be inserted before 10 35 can be inserted before the first element */
Such a tree may also be organized in an array:
12, 11, 10, 8, 9, 7, 6, 1, 2, 4, 3, 5In the following description, keep two pointers into this array in mind: a pointer
node
indicates the location of the next node of the tree, a
pointer child
points to the next element which is a child of the node
pointer. Initially, node
points to the first element, and child
points
to the second element.
*node++ (== 12)
. 12 is the top node. its children are *child++
(11) and *child++
(10), both less than 12.
*node++ (== 11)
), in turn, has *child++
(8)
and *child++
(9) as its children.
*node++ (== 10)
) has *child++
(7)
and *child++
(6) as its children.
*node++ (== 8)
) has *child++
(1)
and *child++
(2) as its children.
*node++ (== 9)
) has children *child++
(4)
and *child++
(3).
*node++ (== 7)
) has
one child *child++
(5)
child
now points beyond the array, the remaining nodes have no
children. So, nodes 6, 1, 2, 4, 3 and 5 don't have children.
Note that the left and right branches are not ordered: 8 is less than 9, but 7 is larger than 6.
The heap is created by traversing a binary tree level-wise, starting from the top node. The top node is 12, at the zeroth level. At the first level we find 11 and 10. At the second level 6, 7, 8 and 9 are found, etc.
Heaps can be created in containers supporting random access. So, a heap is
not, for example, constructed in a list. Heaps can be constructed from an
(unsorted) array (using make_heap()
). The top-element can
be pruned from a heap, followed by reordering the heap (using
pop_heap()
), a new element can be added to the heap,
followed by reordering the heap (using push_heap()
), and
the elements in a heap can be sorted (using sort_heap()
,
which invalidates the heap, though).
The following subsections show the prototypes of the heap-algorithms, the final subsection provides a small example in which the heap algorithms are used.
#include <algorithm>
void make_heap(RandomAccessIterator first,
RandomAccessIterator last);
void make_heap(RandomAccessIterator first,
RandomAccessIterator last,
Compare comp);
[first,
last)
are reordered to form a
max-heap using
operator<()
of the data
type to which the iterators point.
[first,
last)
are reordered to form a max-heap using the binary comparison function
object comp
to compare elements.
make_heap()
.
#include <algorithm>
void pop_heap(RandomAccessIterator first,
RandomAccessIterator last);
void pop_heap(RandomAccessIterator first,
RandomAccessIterator last,
Compare comp);
[first, last)
is moved to last - 1
. Then, the elements in the range
[first, last - 1)
are reordered to form a max-heap using the
operator<()
of the data type to which the iterators point.
[first, last)
is moved to last - 1
. Then, the elements in the range
[first, last - 1)
are reordered to form a max-heap using the binary
comparison function object comp
to compare elements.
pop_heap()
.
#include <algorithm>
void push_heap(RandomAccessIterator first,
RandomAccessIterator last);
void push_heap(RandomAccessIterator first,
RandomAccessIterator last,
Compare comp);
[first,
last - 2)
contains a valid heap, and the element at last - 1
contains an
element to be added to the heap, the elements in the range [first, last
- 1)
are reordered to form a max-heap using the operator<()
of the data
type to which the iterators point.
[first,
last - 2)
contains a valid heap, and the element at last - 1
contains an
element to be added to the heap, the elements in the range [first, last
- 1)
are reordered to form a max-heap using the binary comparison function
object comp
to compare elements.
push_heap()
.
#include <algorithm>
void sort_heap(RandomAccessIterator first,
RandomAccessIterator last);
void sort_heap(RandomAccessIterator first,
RandomAccessIterator last,
Compare comp);
[first, last)
form a valid max-heap, the elements in the range
[first, last)
are sorted using
operator<()
of the data type to
which the iterators point.
[first, last)
form a valid heap, the elements in the range
[first, last)
are sorted using the binary comparison function
object comp
to compare elements.
sort_heap()
.
#include <algorithm> #include <iostream> #include <functional> #include <iterator> void show(int *ia, char const *header) { std::cout << header << ":\n"; std::copy(ia, ia + 20, std::ostream_iterator<int>(std::cout, " ")); std::cout << std::endl; } using namespace std; int main() { int ia[] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20}; make_heap(ia, ia + 20); show(ia, "The values 1-20 in a max-heap"); pop_heap(ia, ia + 20); show(ia, "Removing the first element (now at the end)"); push_heap(ia, ia + 20); show(ia, "Adding 20 (at the end) to the heap again"); sort_heap(ia, ia + 20); show(ia, "Sorting the elements in the heap"); make_heap(ia, ia + 20, greater<int>()); show(ia, "The values 1-20 in a heap, using > (and beyond too)"); pop_heap(ia, ia + 20, greater<int>()); show(ia, "Removing the first element (now at the end)"); push_heap(ia, ia + 20, greater<int>()); show(ia, "Re-adding the removed element"); sort_heap(ia, ia + 20, greater<int>()); show(ia, "Sorting the elements in the heap"); return 0; } /* Generated output: The values 1-20 in a max-heap: 20 19 15 18 11 13 14 17 9 10 2 12 6 3 7 16 8 4 1 5 Removing the first element (now at the end): 19 18 15 17 11 13 14 16 9 10 2 12 6 3 7 5 8 4 1 20 Adding 20 (at the end) to the heap again: 20 19 15 17 18 13 14 16 9 11 2 12 6 3 7 5 8 4 1 10 Sorting the elements in the heap: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 The values 1-20 in a heap, using > (and beyond too): 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Removing the first element (now at the end): 2 4 3 8 5 6 7 16 9 10 11 12 13 14 15 20 17 18 19 1 Re-adding the removed element: 1 2 3 8 4 6 7 16 9 5 11 12 13 14 15 20 17 18 19 10 Sorting the elements in the heap: 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 */