    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}