    001package net.sf.cpsolver.ifs.dbt;
    002
    003import net.sf.cpsolver.ifs.extension.Extension;
    004import net.sf.cpsolver.ifs.heuristics.VariableSelection;
    005import net.sf.cpsolver.ifs.model.Value;
    006import net.sf.cpsolver.ifs.model.Variable;
    007import net.sf.cpsolver.ifs.solution.Solution;
    008import net.sf.cpsolver.ifs.solver.Solver;
    009import net.sf.cpsolver.ifs.util.DataProperties;
    010
    011/**
    012 * Selection of a variable for dynamic backtracking. <br>
    013 * <br>
    014 * <li>Returns null if all variables are assigned. <li>Checks if there is a
    015 * varaible with all values marked as nogood (and pick it if there is any). <li>
    016 * Returns the first unassigned variable. <br>
    017 * <br>
    018 * This IFS solver variable selection heuristics is to be used only in case of
    019 * dynamic backtracking and it has no parameters.
    020 *
    021 *
    022 * @version IFS 1.2 (Iterative Forward Search)<br>
    023 *          Copyright (C) 2006 - 2010 Tomáš Müller<br>
    024 *          <a href="mailto:muller@unitime.org">muller@unitime.org</a><br>
    025 *          <a href="http://muller.unitime.org">http://muller.unitime.org</a><br>
    026 * <br>
    027 *          This library is free software; you can redistribute it and/or modify
    028 *          it under the terms of the GNU Lesser General Public License as
    029 *          published by the Free Software Foundation; either version 3 of the
    030 *          License, or (at your option) any later version. <br>
    031 * <br>
    032 *          This library is distributed in the hope that it will be useful, but
    033 *          WITHOUT ANY WARRANTY; without even the implied warranty of
    034 *          MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
    035 *          Lesser General Public License for more details. <br>
    036 * <br>
    037 *          You should have received a copy of the GNU Lesser General Public
    038 *          License along with this library; if not see
    039 *          <a href='http://www.gnu.org/licenses/'>http://www.gnu.org/licenses/</a>.
    040 */
    041public class DbtVariableSelection<V extends Variable<V, T>, T extends Value<V, T>> implements VariableSelection<V, T> {
    042    private DbtPropagation<V, T> iProp = null;
    043
    044    public DbtVariableSelection(DataProperties properties) {
    045    }
    046
    047    /**
    048     * Heuristics initialization
    049     *
    050     * @see VariableSelection#init(Solver)
    051     */
    052    @Override
    053    public void init(Solver<V, T> solver) {
    054        for (Extension<V, T> extension : solver.getExtensions()) {
    055            if (extension instanceof DbtPropagation<?, ?>) {
    056                iProp = (DbtPropagation<V, T>) extension;
    057            }
    058        }
    059    }
    060
    061    /**
    062     * Variable selection
    063     *
    064     * @see VariableSelection#selectVariable(Solution)
    065     */
    066    @Override
    067    public V selectVariable(Solution<V, T> solution) {
    068        if (solution.getModel().nrUnassignedVariables() == 0) {
    069            return null;
    070        }
    071        if (iProp != null) {
    072            for (V variable : solution.getModel().unassignedVariables()) {
    073                if (iProp.goodValues(variable).isEmpty()) {
    074                    return variable;
    075                }
    076            }
    077        }
    078        return solution.getModel().unassignedVariables().iterator().next();
    079    }
    080
    081}