AC3x.h

// AC3x.h -- The AC-3x filter interface.

/*
 * Copyright (C) 1998 Tudor Hulubei <tudor@hulubei.net>.
 *
 * This library is free software; you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as
 * published by the Free Software Foundation; either version 2, or (at
 * your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA,
 * 02111-1307, USA.
 */

// $Id: AC3x_8h-source.html,v 1.1 2005/05/25 12:37:18 tudor Exp $

#ifndef _CSP_FILTERS_AC3X_H
#define _CSP_FILTERS_AC3X_H


CSP_NAMESPACE_BEGIN(csp);
CSP_NAMESPACE_BEGIN(filters);


class CSP_API AC3x :
    public Filter
{
  public:
    AC3x(Problem& problem, Retraction& retraction, bool optimizeCC = false) :
        Filter(L"Arc Consistency 3x", L"AC-3x", problem, retraction) {
        m_optimizeCC = optimizeCC; }
    ~AC3x() {}

    virtual bool init(
        const vlist_type& uninstantiatedVariables,
        bool propagate = true);
    virtual void done() { Filter::done(); }

    virtual bool restoresArcConsistency() const { return true; }

    virtual bool propagate(
        const vlist_type& uninstantiatedVariables,
        const vlist_type& modifiedVariables,
        const bool keepChanges = true);

  private:
    void queueInit();

    void queueClear();

    void queueMaintain();

    void queuePush(Constraint& c);

    void queuePop();

    bool queueEmpty() const;

    Constraint& queueTop() const;

    Domain m_diffs;

    // The queue of constraints to be processed.
    vector<Constraint*> m_heap;

    // The queue of constraints to be processed.
    deque<Constraint*> m_queue;

    /* Depending on whether or not this is true, we use `m_heap' or
       `m_queue'.  The use of `m_heap' will cut down the number of
       constraint checks, but it is expensive and in practice it
       doesn't seem to be worth the trouble, which is why it is
       turned off.  */
    bool m_optimizeCC;

    // `true' for constraints already in the queue.
    hash_set<const Constraint*> m_inQueue;

    AC3x(const AC3x&);

    AC3x& operator=(const AC3x&);

    /* Return `true' if the unary constraint `constraint' can be
       satisfied.  */
    bool pruneUnaryConstraint(Constraint& constraint);

    /* Make sure the domains of all the variables involved in the
       given constraint have support.  Return `true' on succes (no dwo),
       `false' otherwise.  */
    bool pruneBinaryConstraint(Constraint& c);

    void addRelatedConstraints(Constraint& constraint, Variable& variable);

    void addActiveConstraints(const Variable& variable);
};


CSP_NAMESPACE_END(filters);
CSP_NAMESPACE_END(csp);


#endif // _CSP_FILTERS_AC3X_H

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