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1 /* -*- mode: C++; c-basic-offset: 2; indent-tabs-mode: nil -*- */
2 /*
3  * Main authors:
4  * Christian Schulte <schulte@gecode.org>
5  *
6  * Contributing authors:
7  * Guido Tack <tack@gecode.org>
8  *
9  * Copyright:
10  * Christian Schulte, 2004
11  * Guido Tack, 2004
12  *
13  * Last modified:
14  * $Date: 2013-07-12 18:20:11 +0200 (Fri, 12 Jul 2013) $ by $Author: schulte $
15  * $Revision: 13877 $
16  *
17  * This file is part of Gecode, the generic constraint
18  * development environment:
19  * http://www.gecode.org
20  *
21  * Permission is hereby granted, free of charge, to any person obtaining
22  * a copy of this software and associated documentation files (the
23  * "Software"), to deal in the Software without restriction, including
24  * without limitation the rights to use, copy, modify, merge, publish,
25  * distribute, sublicense, and/or sell copies of the Software, and to
26  * permit persons to whom the Software is furnished to do so, subject to
27  * the following conditions:
28  *
29  * The above copyright notice and this permission notice shall be
30  * included in all copies or substantial portions of the Software.
31  *
32  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
33  * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
34  * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
35  * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
36  * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
37  * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
38  * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
39  *
40  */
41 
42 #ifndef __GECODE_SEARCH_SEQUENTIAL_BAB_HH__
43 #define __GECODE_SEARCH_SEQUENTIAL_BAB_HH__
44 
45 #include <gecode/search.hh>
46 #include <gecode/search/support.hh>
47 #include <gecode/search/worker.hh>
49 
50 namespace Gecode { namespace Search { namespace Sequential {
51 
53  class BAB : public Worker {
54  private:
56  Options opt;
58  Path path;
60  Space* cur;
62  unsigned int d;
64  int mark;
66  Space* best;
67  public:
69  BAB(Space* s, const Options& o);
71  Space* next(void);
73  Statistics statistics(void) const;
75  void reset(Space* s);
77  NoGoods& nogoods(void);
79  ~BAB(void);
80  };
81 
83  BAB::BAB(Space* s, const Options& o)
84  : opt(o), path(static_cast<int>(opt.nogoods_limit)),
85  d(0), mark(0), best(NULL) {
86  if ((s == NULL) || (s->status(*this) == SS_FAILED)) {
87  fail++;
88  cur = NULL;
89  if (!o.clone)
90  delete s;
91  } else {
92  cur = snapshot(s,opt);
93  }
94  }
95 
97  BAB::next(void) {
98  /*
99  * The invariant maintained by the engine is:
100  * For all nodes stored at a depth less than mark, there
101  * is no guarantee of betterness. For those above the mark,
102  * betterness is guaranteed.
103  *
104  * The engine maintains the path on the stack for the current
105  * node to be explored.
106  *
107  */
108  start();
109  while (true) {
110  while (cur) {
111  if (stop(opt))
112  return NULL;
113  node++;
114  switch (cur->status(*this)) {
115  case SS_FAILED:
116  fail++;
117  delete cur;
118  cur = NULL;
119  break;
120  case SS_SOLVED:
121  // Deletes all pending branchers
122  (void) cur->choice();
123  delete best;
124  best = cur;
125  cur = NULL;
126  mark = path.entries();
127  return best->clone();
128  case SS_BRANCH:
129  {
130  Space* c;
131  if ((d == 0) || (d >= opt.c_d)) {
132  c = cur->clone();
133  d = 1;
134  } else {
135  c = NULL;
136  d++;
137  }
138  const Choice* ch = path.push(*this,cur,c);
139  cur->commit(*ch,0);
140  break;
141  }
142  default:
143  GECODE_NEVER;
144  }
145  }
146  // Recompute and add constraint if necessary
147  do {
148  if (!path.next())
149  return NULL;
150  cur = path.recompute(d,opt.a_d,*this,best,mark);
151  } while (cur == NULL);
152  }
153  GECODE_NEVER;
154  return NULL;
155  }
156 
158  BAB::statistics(void) const {
159  return *this;
160  }
161 
162  forceinline void
164  delete best;
165  best = NULL;
166  path.reset();
167  d = mark = 0;
168  delete cur;
169  if ((s == NULL) || (s->status(*this) == SS_FAILED)) {
170  cur = NULL;
171  } else {
172  cur = s;
173  }
174  Worker::reset();
175  }
176 
178  BAB::nogoods(void) {
179  return path;
180  }
181 
182  forceinline
183  BAB::~BAB(void) {
184  path.reset();
185  delete best;
186  delete cur;
187  }
188 
189 }}}
190 
191 #endif
192 
193 // STATISTICS: search-sequential