    001package org.cpsolver.ifs.example.csp;
    002
    003import java.util.Random;
    004import java.util.Set;
    005
    006import org.cpsolver.ifs.assignment.Assignment;
    007import org.cpsolver.ifs.model.BinaryConstraint;
    008
    009
    010/**
    011 * CSP binary constraint. <br>
    012 * <br>
    013 * This class only implements the generation of a binary CSP constraint and the
    014 * consistency check.
    015 *
    016 * @version IFS 1.3 (Iterative Forward Search)<br>
    017 *          Copyright (C) 2006 - 2014 Tomáš Müller<br>
    018 *          <a href="mailto:muller@unitime.org">muller@unitime.org</a><br>
    019 *          <a href="http://muller.unitime.org">http://muller.unitime.org</a><br>
    020 * <br>
    021 *          This library is free software; you can redistribute it and/or modify
    022 *          it under the terms of the GNU Lesser General Public License as
    023 *          published by the Free Software Foundation; either version 3 of the
    024 *          License, or (at your option) any later version. <br>
    025 * <br>
    026 *          This library is distributed in the hope that it will be useful, but
    027 *          WITHOUT ANY WARRANTY; without even the implied warranty of
    028 *          MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
    029 *          Lesser General Public License for more details. <br>
    030 * <br>
    031 *          You should have received a copy of the GNU Lesser General Public
    032 *          License along with this library; if not see
    033 *          <a href='http://www.gnu.org/licenses/'>http://www.gnu.org/licenses/</a>.
    034 */
    035public class CSPBinaryConstraint extends BinaryConstraint<CSPVariable, CSPValue> {
    036    private boolean iIsConsistent[][] = null;
    037    private int iNrCompatiblePairs;
    038
    039    /**
    040     * Constructor
    041     * @param id constraint id
    042     * @param nrCompatiblePairs
    043     *            number of compatible pairs of values in the constraint
    044     */
    045    public CSPBinaryConstraint(int id, int nrCompatiblePairs) {
    046        super();
    047        iId = id;
    048        iNrCompatiblePairs = nrCompatiblePairs;
    049    }
    050
    051    private void swap(int[][] allPairs, int first, int second) {
    052        int[] a = allPairs[first];
    053        allPairs[first] = allPairs[second];
    054        allPairs[second] = a;
    055    }
    056
    057    /**
    058     * Initializes the constraint. Randomly generates the given number of
    059     * compatible pairs of values.
    060     *
    061     * @param rndNumGen
    062     *            random number generator
    063     */
    064    public void init(Random rndNumGen) {
    065        int numberOfAllPairs = first().values(null).size() * second().values(null).size();
    066        int[][] allPairs = new int[numberOfAllPairs][];
    067        int idx = 0;
    068
    069        iIsConsistent = new boolean[first().values(null).size()][second().values(null).size()];
    070
    071        for (CSPValue v1 : first().values(null)) {
    072            for (CSPValue v2 : second().values(null)) {
    073                iIsConsistent[(int) v1.toDouble()][(int) v2.toDouble()] = false;
    074                allPairs[idx++] = new int[] { (int) v1.toDouble(), (int) v2.toDouble() };
    075            }
    076        }
    077
    078        for (int i = 0; i < iNrCompatiblePairs; i++) {
    079            swap(allPairs, i, i + (int) (rndNumGen.nextDouble() * (numberOfAllPairs - i)));
    080            iIsConsistent[allPairs[i][0]][allPairs[i][1]] = true;
    081        }
    082    }
    083
    084    /**
    085     * True if the pair of given values is compatible.
    086     */
    087    @Override
    088    public boolean isConsistent(CSPValue value1, CSPValue value2) {
    089        if (value1 == null || value2 == null)
    090            return true;
    091        if (isFirst(value1.variable())) {
    092            return iIsConsistent[(int) value1.toDouble()][(int) value2.toDouble()];
    093        } else {
    094            return iIsConsistent[(int) value2.toDouble()][(int) value1.toDouble()];
    095        }
    096    }
    097
    098    /**
    099     * Add the other variable to the set of conflicts, if it is not compatible
    100     * with the given value.
    101     */
    102    @Override
    103    public void computeConflicts(Assignment<CSPVariable, CSPValue> assignment, CSPValue aValue, Set<CSPValue> conflicts) {
    104        if (isFirst(aValue.variable())) {
    105            if (!isConsistent(aValue, assignment.getValue(second()))) {
    106                conflicts.add(assignment.getValue(second()));
    107            }
    108        } else {
    109            if (!isConsistent(assignment.getValue(first()), aValue)) {
    110                conflicts.add(assignment.getValue(first()));
    111            }
    112        }
    113    }
    114
    115    @Override
    116    public String getName() {
    117        return "C" + getId();
    118    }
    119}