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 * @author  Tomáš Müller
026 * @version IFS 1.3 (Iterative Forward Search)<br>
027 *          Copyright (C) 2006 - 2014 Tomáš Müller<br>
028 *          <a href="mailto:muller@unitime.org">muller@unitime.org</a><br>
029 *          <a href="http://muller.unitime.org">http://muller.unitime.org</a><br>
030 * <br>
031 *          This library is free software; you can redistribute it and/or modify
032 *          it under the terms of the GNU Lesser General Public License as
033 *          published by the Free Software Foundation; either version 3 of the
034 *          License, or (at your option) any later version. <br>
035 * <br>
036 *          This library is distributed in the hope that it will be useful, but
037 *          WITHOUT ANY WARRANTY; without even the implied warranty of
038 *          MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
039 *          Lesser General Public License for more details. <br>
040 * <br>
041 *          You should have received a copy of the GNU Lesser General Public
042 *          License along with this library; if not see
043 *          <a href='http://www.gnu.org/licenses/'>http://www.gnu.org/licenses/</a>.
044 * @param <V> Variable
045 * @param <T> Value
046 */
047public class DbtVariableSelection<V extends Variable<V, T>, T extends Value<V, T>> implements VariableSelection<V, T> {
048    private DbtPropagation<V, T> iProp = null;
049
050    public DbtVariableSelection(DataProperties properties) {
051    }
052
053    /**
054     * Heuristics initialization
055     * 
056     * @see VariableSelection#init(Solver)
057     */
058    @Override
059    public void init(Solver<V, T> solver) {
060        for (Extension<V, T> extension : solver.getExtensions()) {
061            if (extension instanceof DbtPropagation<?, ?>) {
062                iProp = (DbtPropagation<V, T>) extension;
063            }
064        }
065    }
066
067    /**
068     * Variable selection
069     * 
070     * @see VariableSelection#selectVariable(Solution)
071     */
072    @Override
073    public V selectVariable(Solution<V, T> solution) {
074        if (solution.getAssignment().nrAssignedVariables() == solution.getModel().variables().size()) {
075            return null;
076        }
077        if (iProp != null) {
078            for (V variable : solution.getAssignment().unassignedVariables(solution.getModel())) {
079                if (iProp.goodValues(solution.getAssignment(), variable).isEmpty()) {
080                    return variable;
081                }
082            }
083        }
084        return ToolBox.random(solution.getAssignment().unassignedVariables(solution.getModel()));
085    }
086
087}