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}