001package org.cpsolver.ifs.dbt;
002
003import org.cpsolver.ifs.extension.Extension;
004import org.cpsolver.ifs.heuristics.VariableSelection;
005import org.cpsolver.ifs.model.Value;
006import org.cpsolver.ifs.model.Variable;
007import org.cpsolver.ifs.solution.Solution;
008import org.cpsolver.ifs.solver.Solver;
009import org.cpsolver.ifs.util.DataProperties;
010import org.cpsolver.ifs.util.ToolBox;
011
012/**
013 * Selection of a variable for dynamic backtracking. <br>
014 * <br>
015 * <ul>
016 * <li>Returns null if all variables are assigned.
017 * <li>Checks if there is a varaible with all values marked as nogood (and pick it if there is any).
018 * <li> Returns the first unassigned variable.
019 * </ul>
020 * <br>
021 * This IFS solver variable selection heuristics is to be used only in case of
022 * dynamic backtracking and it has no parameters.
023 * 
024 * 
025 * @version IFS 1.3 (Iterative Forward Search)<br>
026 *          Copyright (C) 2006 - 2014 Tomáš Müller<br>
027 *          <a href="mailto:muller@unitime.org">muller@unitime.org</a><br>
028 *          <a href="http://muller.unitime.org">http://muller.unitime.org</a><br>
029 * <br>
030 *          This library is free software; you can redistribute it and/or modify
031 *          it under the terms of the GNU Lesser General Public License as
032 *          published by the Free Software Foundation; either version 3 of the
033 *          License, or (at your option) any later version. <br>
034 * <br>
035 *          This library is distributed in the hope that it will be useful, but
036 *          WITHOUT ANY WARRANTY; without even the implied warranty of
037 *          MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
038 *          Lesser General Public License for more details. <br>
039 * <br>
040 *          You should have received a copy of the GNU Lesser General Public
041 *          License along with this library; if not see
042 *          <a href='http://www.gnu.org/licenses/'>http://www.gnu.org/licenses/</a>.
043 * @param <V> Variable
044 * @param <T> Value
045 */
046public class DbtVariableSelection<V extends Variable<V, T>, T extends Value<V, T>> implements VariableSelection<V, T> {
047    private DbtPropagation<V, T> iProp = null;
048
049    public DbtVariableSelection(DataProperties properties) {
050    }
051
052    /**
053     * Heuristics initialization
054     * 
055     * @see VariableSelection#init(Solver)
056     */
057    @Override
058    public void init(Solver<V, T> solver) {
059        for (Extension<V, T> extension : solver.getExtensions()) {
060            if (extension instanceof DbtPropagation<?, ?>) {
061                iProp = (DbtPropagation<V, T>) extension;
062            }
063        }
064    }
065
066    /**
067     * Variable selection
068     * 
069     * @see VariableSelection#selectVariable(Solution)
070     */
071    @Override
072    public V selectVariable(Solution<V, T> solution) {
073        if (solution.getAssignment().nrAssignedVariables() == solution.getModel().variables().size()) {
074            return null;
075        }
076        if (iProp != null) {
077            for (V variable : solution.getAssignment().unassignedVariables(solution.getModel())) {
078                if (iProp.goodValues(solution.getAssignment(), variable).isEmpty()) {
079                    return variable;
080                }
081            }
082        }
083        return ToolBox.random(solution.getAssignment().unassignedVariables(solution.getModel()));
084    }
085
086}