001package org.cpsolver.ifs.algorithms.neighbourhoods;
002
003import java.util.List;
004
005import org.cpsolver.ifs.assignment.Assignment;
006import org.cpsolver.ifs.heuristics.NeighbourSelection;
007import org.cpsolver.ifs.model.Model;
008import org.cpsolver.ifs.model.Neighbour;
009import org.cpsolver.ifs.model.SimpleNeighbour;
010import org.cpsolver.ifs.model.Value;
011import org.cpsolver.ifs.model.Variable;
012import org.cpsolver.ifs.solution.Solution;
013import org.cpsolver.ifs.solver.Solver;
014import org.cpsolver.ifs.util.DataProperties;
015import org.cpsolver.ifs.util.ToolBox;
016
017
018/**
019 * Try to assign a variable with a new value. A variable is selected randomly, a
020 * different (available) value is randomly selected for the variable -- the variable is
021 * assigned with the new value if there is no conflict.
022 * <br>
023 * 
024 * @version IFS 1.3 (Iterative Forward Search)<br>
025 *          Copyright (C) 2014 Tomáš Müller<br>
026 *          <a href="mailto:muller@unitime.org">muller@unitime.org</a><br>
027 *          <a href="http://muller.unitime.org">http://muller.unitime.org</a><br>
028 * <br>
029 *          This library is free software; you can redistribute it and/or modify
030 *          it under the terms of the GNU Lesser General Public License as
031 *          published by the Free Software Foundation; either version 3 of the
032 *          License, or (at your option) any later version. <br>
033 * <br>
034 *          This library is distributed in the hope that it will be useful, but
035 *          WITHOUT ANY WARRANTY; without even the implied warranty of
036 *          MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
037 *          Lesser General Public License for more details. <br>
038 * <br>
039 *          You should have received a copy of the GNU Lesser General Public
040 *          License along with this library; if not see
041 *          <a href='http://www.gnu.org/licenses/'>http://www.gnu.org/licenses/</a>.
042 * @param <V> Variable
043 * @param <T> Value
044 */
045public class RandomMove<V extends Variable<V, T>, T extends Value<V, T>> implements NeighbourSelection<V, T>, HillClimberSelection {
046    protected boolean iHC = false;
047    
048    public RandomMove(DataProperties config) {
049    }
050
051    @Override
052    public void setHcMode(boolean hcMode) {
053        iHC = hcMode;
054    }
055
056    @Override
057    public void init(Solver<V, T> solver) {
058    }
059
060    @Override
061    public Neighbour<V, T> selectNeighbour(Solution<V, T> solution) {
062        Model<V, T> model = solution.getModel();
063        Assignment<V, T> assignment = solution.getAssignment();
064        int varIdx = ToolBox.random(model.variables().size());
065        for (int i = 0; i < model.variables().size(); i++) {
066            V variable = model.variables().get((i + varIdx) % model.variables().size());
067            List<T> values = variable.values(solution.getAssignment());
068            if (values.isEmpty()) continue;
069            int valIdx = ToolBox.random(values.size());
070            for (int j = 0; j < values.size(); j++) {
071                T value = values.get((j + valIdx) % values.size());
072                if (!model.inConflict(assignment, value)) {
073                    SimpleNeighbour<V, T> n = new SimpleNeighbour<V, T>(variable, value);
074                    if (!iHC || n.value(assignment) <= 0) return n;
075                }
076            }
077        }
078        return null;
079    }
080}