001package net.sf.cpsolver.ifs.heuristics;
002
003import java.util.ArrayList;
004import java.util.List;
005
006import net.sf.cpsolver.ifs.model.Neighbour;
007import net.sf.cpsolver.ifs.model.Value;
008import net.sf.cpsolver.ifs.model.Variable;
009import net.sf.cpsolver.ifs.solution.Solution;
010import net.sf.cpsolver.ifs.solver.Solver;
011import net.sf.cpsolver.ifs.util.DataProperties;
012
013import org.apache.log4j.Logger;
014
015/**
016 * A round robin neighbour selection. Two or more {@link NeighbourSelection}
017 * needs to be registered within the selection. This selection criterion takes
018 * the registered neighbour selections one by one and performs
019 * {@link NeighbourSelection#init(Solver)} and then it is using
020 * {@link NeighbourSelection#selectNeighbour(Solution)} to select a neighbour.
021 * When null is returned by the underlaying selection, next registered neighbour
022 * selection is initialized and used for the following selection(s). If the last
023 * registered selection returns null, the selection is returned to the first
024 * registered neighbour selection (it is initialized before used again).
025 * 
026 * <br>
027 * <br>
028 * 
029 * @version StudentSct 1.2 (Student Sectioning)<br>
030 *          Copyright (C) 2007 - 2010 Tomáš Müller<br>
031 *          <a href="mailto:muller@unitime.org">muller@unitime.org</a><br>
032 *          <a href="http://muller.unitime.org">http://muller.unitime.org</a><br>
033 * <br>
034 *          This library is free software; you can redistribute it and/or modify
035 *          it under the terms of the GNU Lesser General Public License as
036 *          published by the Free Software Foundation; either version 3 of the
037 *          License, or (at your option) any later version. <br>
038 * <br>
039 *          This library is distributed in the hope that it will be useful, but
040 *          WITHOUT ANY WARRANTY; without even the implied warranty of
041 *          MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
042 *          Lesser General Public License for more details. <br>
043 * <br>
044 *          You should have received a copy of the GNU Lesser General Public
045 *          License along with this library; if not see
046 *          <a href='http://www.gnu.org/licenses/'>http://www.gnu.org/licenses/</a>.
047 */
048
049public class RoundRobinNeighbourSelection<V extends Variable<V, T>, T extends Value<V, T>> extends
050        StandardNeighbourSelection<V, T> {
051    private static Logger sLogger = Logger.getLogger(RoundRobinNeighbourSelection.class);
052    private int iSelectionIdx = -1;
053    private List<NeighbourSelection<V, T>> iSelections = new ArrayList<NeighbourSelection<V, T>>();
054    private Solver<V, T> iSolver = null;
055
056    /**
057     * Constructor
058     * 
059     * @param properties
060     *            configuration
061     * @throws Exception
062     */
063    public RoundRobinNeighbourSelection(DataProperties properties) throws Exception {
064        super(properties);
065    }
066
067    /** Register a neighbour selection */
068    public void registerSelection(NeighbourSelection<V, T> selection) {
069        iSelections.add(selection);
070    }
071
072    /** Initialization */
073    @Override
074    public void init(Solver<V, T> solver) {
075        super.init(solver);
076        iSolver = solver;
077    }
078
079    /**
080     * Select neighbour. A first registered selections is initialized and used
081     * until it returns null, then the second registered selections is
082     * initialized and used and vice versa.
083     */
084    @Override
085    public Neighbour<V, T> selectNeighbour(Solution<V, T> solution) {
086        if (iSelectionIdx == -1) {
087            iSelectionIdx = 0;
088            iSelections.get(iSelectionIdx).init(iSolver);
089        }
090        while (true) {
091            NeighbourSelection<V, T> selection = iSelections.get(iSelectionIdx);
092            Neighbour<V, T> neighbour = selection.selectNeighbour(solution);
093            if (neighbour != null)
094                return neighbour;
095            changeSelection(solution);
096        }
097    }
098
099    /** Change selection */
100    public void changeSelection(Solution<V, T> solution) {
101        iSelectionIdx = (1 + iSelectionIdx) % iSelections.size();
102        sLogger.debug("Phase changed to " + (iSelectionIdx + 1));
103        if (solution.getBestInfo() == null || iSolver.getSolutionComparator().isBetterThanBestSolution(solution))
104            solution.saveBest();
105        iSelections.get(iSelectionIdx).init(iSolver);
106    }
107}