bab.hh

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/* -*- mode: C++; c-basic-offset: 2; indent-tabs-mode: nil -*- */
/*
 *  Main authors:
 *     Christian Schulte <schulte@gecode.org>
 *
 *  Contributing authors:
 *     Guido Tack <tack@gecode.org>
 *
 *  Copyright:
 *     Christian Schulte, 2004
 *     Guido Tack, 2004
 *
 *  Last modified:
 *     $Date: 2016-04-19 17:19:45 +0200 (Tue, 19 Apr 2016) $ by $Author: schulte $
 *     $Revision: 14967 $
 *
 *  This file is part of Gecode, the generic constraint
 *  development environment:
 *     http://www.gecode.org
 *
 *  Permission is hereby granted, free of charge, to any person obtaining
 *  a copy of this software and associated documentation files (the
 *  "Software"), to deal in the Software without restriction, including
 *  without limitation the rights to use, copy, modify, merge, publish,
 *  distribute, sublicense, and/or sell copies of the Software, and to
 *  permit persons to whom the Software is furnished to do so, subject to
 *  the following conditions:
 *
 *  The above copyright notice and this permission notice shall be
 *  included in all copies or substantial portions of the Software.
 *
 *  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 *  EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 *  MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 *  NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
 *  LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
 *  OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
 *  WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 *
 */

#ifndef __GECODE_SEARCH_SEQUENTIAL_BAB_HH__
#define __GECODE_SEARCH_SEQUENTIAL_BAB_HH__

#include <gecode/search.hh>
#include <gecode/search/support.hh>
#include <gecode/search/worker.hh>
#include <gecode/search/sequential/path.hh>

namespace Gecode { namespace Search { namespace Sequential {

  class BAB : public Worker {
  private:
    Options opt;
    Path path;
    Space* cur;
    unsigned int d;
    int mark;
    Space* best;
  public:
    BAB(Space* s, const Options& o);
    Space* next(void);
    Statistics statistics(void) const;
    void constrain(const Space& b);
    void reset(Space* s);
    NoGoods& nogoods(void);
    ~BAB(void);
  };

  forceinline
  BAB::BAB(Space* s, const Options& o)
    : opt(o), path(opt.nogoods_limit), d(0), mark(0), best(NULL) {
    if ((s == NULL) || (s->status(*this) == SS_FAILED)) {
      fail++;
      cur = NULL;
      if (!o.clone)
        delete s;
    } else {
      cur = snapshot(s,opt);
    }
  }

  forceinline Space*
  BAB::next(void) {
    /*
     * The engine maintains the following invariant:
     *  - If the current space (cur) is not NULL, the path always points
     *    to exactly that space.
     *  - If the current space (cur) is NULL, the path always points
     *    to the next space (if there is any).
     *
     * This invariant is needed so that no-goods can be extracted properly
     * when the engine is stopped or has found a solution.
     *
     * An additional invariant maintained by the engine is:
     *   For all nodes stored at a depth less than mark, there
     *   is no guarantee of betterness. For those above the mark,
     *   betterness is guaranteed.
     *
     */
    start();
    while (true) {
      if (stop(opt))
        return NULL;
      // Recompute and add constraint if necessary
      while (cur == NULL) {
        if (path.empty())
          return NULL;
        cur = path.recompute(d,opt.a_d,*this,*best,mark);
        if (cur != NULL)
          break;
        path.next();
      }
      node++;
      switch (cur->status(*this)) {
      case SS_FAILED:
        fail++;
        delete cur;
        cur = NULL;
        path.next();
        break;
      case SS_SOLVED:
        // Deletes all pending branchers
        (void) cur->choice();
        delete best;
        best = cur;
        cur = NULL;
        path.next();
        mark = path.entries();
        return best->clone();
      case SS_BRANCH:
        {
          Space* c;
          if ((d == 0) || (d >= opt.c_d)) {
            c = cur->clone();
            d = 1;
          } else {
            c = NULL;
            d++;
          }
          const Choice* ch = path.push(*this,cur,c);
          cur->commit(*ch,0);
          break;
        }
      default:
        GECODE_NEVER;
      }
    }
    GECODE_NEVER;
    return NULL;
  }

  forceinline Statistics
  BAB::statistics(void) const {
    return *this;
  }

  forceinline void
  BAB::constrain(const Space& b) {
    if (best != NULL) {
      // Check whether b is in fact better than best
      best->constrain(b);
      if (best->status(*this) != SS_FAILED)
        return;
      else
        delete best;
    }
    best = b.clone();
    if (cur != NULL)
      cur->constrain(b);
    mark = path.entries();
  }

  forceinline void
  BAB::reset(Space* s) {
    delete best;
    best = NULL;
    path.reset();
    d = 0;
    mark = 0;
    delete cur;
    if ((s == NULL) || (s->status(*this) == SS_FAILED)) {
      delete s;
      cur = NULL;
    } else {
      cur = s;
    }
    Worker::reset();
  }

  forceinline NoGoods&
  BAB::nogoods(void) {
    return path;
  }

  forceinline
  BAB::~BAB(void) {
    path.reset();
    delete best;
    delete cur;
  }

}}}

#endif

// STATISTICS: search-sequential