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00001 /* -*- mode: C++; c-basic-offset: 2; indent-tabs-mode: nil -*- */
00002 /*
00003  *  Main authors:
00004  *     Christian Schulte <schulte@gecode.org>
00005  *
00006  *  Contributing authors:
00007  *     Guido Tack <tack@gecode.org>
00008  *
00009  *  Copyright:
00010  *     Christian Schulte, 2004
00011  *     Guido Tack, 2004
00012  *
00013  *  Last modified:
00014  *     $Date: 2013-10-24 16:42:20 +0200 (Thu, 24 Oct 2013) $ by $Author: schulte $
00015  *     $Revision: 14030 $
00016  *
00017  *  This file is part of Gecode, the generic constraint
00018  *  development environment:
00019  *     http://www.gecode.org
00020  *
00021  *  Permission is hereby granted, free of charge, to any person obtaining
00022  *  a copy of this software and associated documentation files (the
00023  *  "Software"), to deal in the Software without restriction, including
00024  *  without limitation the rights to use, copy, modify, merge, publish,
00025  *  distribute, sublicense, and/or sell copies of the Software, and to
00026  *  permit persons to whom the Software is furnished to do so, subject to
00027  *  the following conditions:
00028  *
00029  *  The above copyright notice and this permission notice shall be
00030  *  included in all copies or substantial portions of the Software.
00031  *
00032  *  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
00033  *  EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
00034  *  MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
00035  *  NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
00036  *  LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
00037  *  OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
00038  *  WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
00039  *
00040  */
00041 
00042 #ifndef __GECODE_SEARCH_SEQUENTIAL_BAB_HH__
00043 #define __GECODE_SEARCH_SEQUENTIAL_BAB_HH__
00044 
00045 #include <gecode/search.hh>
00046 #include <gecode/search/support.hh>
00047 #include <gecode/search/worker.hh>
00048 #include <gecode/search/sequential/path.hh>
00049 
00050 namespace Gecode { namespace Search { namespace Sequential {
00051 
00053   class BAB : public Worker {
00054   private:
00056     Options opt;
00058     Path path;
00060     Space* cur;
00062     unsigned int d;
00064     int mark;
00066     Space* best;
00067   public:
00069     BAB(Space* s, const Options& o);
00071     Space* next(void);
00073     Statistics statistics(void) const;
00075     void reset(Space* s);
00077     NoGoods& nogoods(void);
00079     ~BAB(void);
00080   };
00081 
00082   forceinline 
00083   BAB::BAB(Space* s, const Options& o)
00084     : opt(o), path(static_cast<int>(opt.nogoods_limit)), 
00085       d(0), mark(0), best(NULL) {
00086     if ((s == NULL) || (s->status(*this) == SS_FAILED)) {
00087       fail++;
00088       cur = NULL;
00089       if (!o.clone)
00090         delete s;
00091     } else {
00092       cur = snapshot(s,opt);
00093     }
00094   }
00095 
00096   forceinline Space*
00097   BAB::next(void) {
00098     /*
00099      * The invariant maintained by the engine is:
00100      *   For all nodes stored at a depth less than mark, there
00101      *   is no guarantee of betterness. For those above the mark,
00102      *   betterness is guaranteed.
00103      *
00104      * The engine maintains the path on the stack for the current
00105      * node to be explored.
00106      *
00107      */
00108     start();
00109     while (true) {
00110       while (cur) {
00111         if (stop(opt))
00112           return NULL;
00113         node++;
00114         switch (cur->status(*this)) {
00115         case SS_FAILED:
00116           fail++;
00117           delete cur;
00118           cur = NULL;
00119           break;
00120         case SS_SOLVED:
00121           // Deletes all pending branchers
00122           (void) cur->choice();
00123           delete best;
00124           best = cur;
00125           cur = NULL;
00126           mark = path.entries();
00127           return best->clone();
00128         case SS_BRANCH:
00129           {
00130             Space* c;
00131             if ((d == 0) || (d >= opt.c_d)) {
00132               c = cur->clone();
00133               d = 1;
00134             } else {
00135               c = NULL;
00136               d++;
00137             }
00138             const Choice* ch = path.push(*this,cur,c);
00139             cur->commit(*ch,0);
00140             break;
00141           }
00142         default:
00143           GECODE_NEVER;
00144         }
00145       }
00146       // Recompute and add constraint if necessary
00147       do {
00148         if (!path.next())
00149           return NULL;
00150         cur = path.recompute(d,opt.a_d,*this,best,mark);
00151       } while (cur == NULL);
00152     }
00153     GECODE_NEVER;
00154     return NULL;
00155   }
00156 
00157   forceinline Statistics
00158   BAB::statistics(void) const {
00159     return *this;
00160   }
00161 
00162   forceinline void
00163   BAB::reset(Space* s) { 
00164     delete best;
00165     best = NULL;
00166     path.reset();
00167     d = mark = 0U;
00168     delete cur;
00169     if ((s == NULL) || (s->status(*this) == SS_FAILED)) {
00170       cur = NULL;
00171     } else {
00172       cur = s;
00173     }
00174     Worker::reset();
00175   }
00176 
00177   forceinline NoGoods&
00178   BAB::nogoods(void) {
00179     return path;
00180   }
00181 
00182   forceinline 
00183   BAB::~BAB(void) {
00184     path.reset();
00185     delete best;
00186     delete cur;
00187   }
00188 
00189 }}}
00190 
00191 #endif
00192 
00193 // STATISTICS: search-sequential