    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 * @author  Tomáš Müller
    017 * @version IFS 1.3 (Iterative Forward Search)<br>
    018 *          Copyright (C) 2006 - 2014 Tomáš Müller<br>
    019 *          <a href="mailto:muller@unitime.org">muller@unitime.org</a><br>
    020 *          <a href="http://muller.unitime.org">http://muller.unitime.org</a><br>
    021 * <br>
    022 *          This library is free software; you can redistribute it and/or modify
    023 *          it under the terms of the GNU Lesser General Public License as
    024 *          published by the Free Software Foundation; either version 3 of the
    025 *          License, or (at your option) any later version. <br>
    026 * <br>
    027 *          This library is distributed in the hope that it will be useful, but
    028 *          WITHOUT ANY WARRANTY; without even the implied warranty of
    029 *          MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
    030 *          Lesser General Public License for more details. <br>
    031 * <br>
    032 *          You should have received a copy of the GNU Lesser General Public
    033 *          License along with this library; if not see
    034 *          <a href='http://www.gnu.org/licenses/'>http://www.gnu.org/licenses/</a>.
    035 */
    036public class CSPBinaryConstraint extends BinaryConstraint<CSPVariable, CSPValue> {
    037    private boolean iIsConsistent[][] = null;
    038    private int iNrCompatiblePairs;
    039
    040    /**
    041     * Constructor
    042     * @param id constraint id
    043     * @param nrCompatiblePairs
    044     *            number of compatible pairs of values in the constraint
    045     */
    046    public CSPBinaryConstraint(int id, int nrCompatiblePairs) {
    047        super();
    048        iId = id;
    049        iNrCompatiblePairs = nrCompatiblePairs;
    050    }
    051
    052    private void swap(int[][] allPairs, int first, int second) {
    053        int[] a = allPairs[first];
    054        allPairs[first] = allPairs[second];
    055        allPairs[second] = a;
    056    }
    057
    058    /**
    059     * Initializes the constraint. Randomly generates the given number of
    060     * compatible pairs of values.
    061     *
    062     * @param rndNumGen
    063     *            random number generator
    064     */
    065    public void init(Random rndNumGen) {
    066        int numberOfAllPairs = first().values(null).size() * second().values(null).size();
    067        int[][] allPairs = new int[numberOfAllPairs][];
    068        int idx = 0;
    069
    070        iIsConsistent = new boolean[first().values(null).size()][second().values(null).size()];
    071
    072        for (CSPValue v1 : first().values(null)) {
    073            for (CSPValue v2 : second().values(null)) {
    074                iIsConsistent[(int) v1.toDouble()][(int) v2.toDouble()] = false;
    075                allPairs[idx++] = new int[] { (int) v1.toDouble(), (int) v2.toDouble() };
    076            }
    077        }
    078
    079        for (int i = 0; i < iNrCompatiblePairs; i++) {
    080            swap(allPairs, i, i + (int) (rndNumGen.nextDouble() * (numberOfAllPairs - i)));
    081            iIsConsistent[allPairs[i][0]][allPairs[i][1]] = true;
    082        }
    083    }
    084
    085    /**
    086     * True if the pair of given values is compatible.
    087     */
    088    @Override
    089    public boolean isConsistent(CSPValue value1, CSPValue value2) {
    090        if (value1 == null || value2 == null)
    091            return true;
    092        if (isFirst(value1.variable())) {
    093            return iIsConsistent[(int) value1.toDouble()][(int) value2.toDouble()];
    094        } else {
    095            return iIsConsistent[(int) value2.toDouble()][(int) value1.toDouble()];
    096        }
    097    }
    098
    099    /**
    100     * Add the other variable to the set of conflicts, if it is not compatible
    101     * with the given value.
    102     */
    103    @Override
    104    public void computeConflicts(Assignment<CSPVariable, CSPValue> assignment, CSPValue aValue, Set<CSPValue> conflicts) {
    105        if (isFirst(aValue.variable())) {
    106            if (!isConsistent(aValue, assignment.getValue(second()))) {
    107                conflicts.add(assignment.getValue(second()));
    108            }
    109        } else {
    110            if (!isConsistent(assignment.getValue(first()), aValue)) {
    111                conflicts.add(assignment.getValue(first()));
    112            }
    113        }
    114    }
    115
    116    @Override
    117    public String getName() {
    118        return "C" + getId();
    119    }
    120}