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bab.hh
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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: 2011-09-02 19:00:55 +1000 (Fri, 02 Sep 2011) $ by $Author: tack $
15  * $Revision: 12387 $
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, size_t sz, const Options& o);
71  Space* next(void);
73  Statistics statistics(void) const;
75  ~BAB(void);
76  };
77 
79  BAB::BAB(Space* s, size_t sz, const Options& o)
80  : Worker(sz), opt(o), d(0), mark(0), best(NULL) {
81  current(s);
82  if (s->status(*this) == SS_FAILED) {
83  fail++;
84  cur = NULL;
85  if (!o.clone)
86  delete s;
87  } else {
88  cur = snapshot(s,opt);
89  }
90  current(NULL);
91  current(cur);
92  }
93 
95  BAB::next(void) {
96  /*
97  * The invariant maintained by the engine is:
98  * For all nodes stored at a depth less than mark, there
99  * is no guarantee of betterness. For those above the mark,
100  * betterness is guaranteed.
101  *
102  * The engine maintains the path on the stack for the current
103  * node to be explored.
104  *
105  */
106  start();
107  while (true) {
108  while (cur) {
109  if (stop(opt,path.size()))
110  return NULL;
111  node++;
112  switch (cur->status(*this)) {
113  case SS_FAILED:
114  fail++;
115  delete cur;
116  cur = NULL;
117  Worker::current(NULL);
118  break;
119  case SS_SOLVED:
120  // Deletes all pending branchers
121  (void) cur->choice();
122  delete best;
123  best = cur;
124  cur = NULL;
125  mark = path.entries();
126  Worker::current(NULL);
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  Worker::push(c,ch);
140  cur->commit(*ch,0);
141  break;
142  }
143  default:
144  GECODE_NEVER;
145  }
146  }
147  // Recompute and add constraint if necessary
148  do {
149  if (!path.next(*this))
150  return NULL;
151  cur = path.recompute(d,opt.a_d,*this,best,mark);
152  } while (cur == NULL);
153  Worker::current(cur);
154  }
155  GECODE_NEVER;
156  return NULL;
157  }
158 
160  BAB::statistics(void) const {
161  Statistics s = *this;
162  s.memory += path.size();
163  return s;
164  }
165 
166  forceinline
167  BAB::~BAB(void) {
168  path.reset();
169  delete best;
170  delete cur;
171  }
172 
173 }}}
174 
175 #endif
176 
177 // STATISTICS: search-sequential