    001package net.sf.cpsolver.exam.heuristics;
    002
    003import net.sf.cpsolver.exam.model.Exam;
    004import net.sf.cpsolver.exam.model.ExamModel;
    005import net.sf.cpsolver.exam.model.ExamPlacement;
    006import net.sf.cpsolver.ifs.heuristics.VariableSelection;
    007import net.sf.cpsolver.ifs.model.Variable;
    008import net.sf.cpsolver.ifs.solution.Solution;
    009import net.sf.cpsolver.ifs.solver.Solver;
    010import net.sf.cpsolver.ifs.util.DataProperties;
    011import net.sf.cpsolver.ifs.util.ToolBox;
    012
    013/**
    014 * Unassigned variable selection. The "biggest" variable (using
    015 * {@link Variable#compareTo(Object)}) unassigned variable is selected. One is
    016 * selected randomly if there are more than one of such variables.
    017 *
    018 * @version ExamTT 1.2 (Examination Timetabling)<br>
    019 *          Copyright (C) 2008 - 2010 Tomáš Müller<br>
    020 *          <a href="mailto:muller@unitime.org">muller@unitime.org</a><br>
    021 *          <a href="http://muller.unitime.org">http://muller.unitime.org</a><br>
    022 * <br>
    023 *          This library is free software; you can redistribute it and/or modify
    024 *          it under the terms of the GNU Lesser General Public License as
    025 *          published by the Free Software Foundation; either version 3 of the
    026 *          License, or (at your option) any later version. <br>
    027 * <br>
    028 *          This library is distributed in the hope that it will be useful, but
    029 *          WITHOUT ANY WARRANTY; without even the implied warranty of
    030 *          MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
    031 *          Lesser General Public License for more details. <br>
    032 * <br>
    033 *          You should have received a copy of the GNU Lesser General Public
    034 *          License along with this library; if not see
    035 *          <a href='http://www.gnu.org/licenses/'>http://www.gnu.org/licenses/</a>.
    036 */
    037public class ExamUnassignedVariableSelection implements VariableSelection<Exam, ExamPlacement> {
    038    private boolean iRandomSelection = true;
    039
    040    /** Constructor */
    041    public ExamUnassignedVariableSelection(DataProperties properties) {
    042        iRandomSelection = properties.getPropertyBoolean("ExamUnassignedVariableSelection.random", iRandomSelection);
    043    }
    044
    045    /** Initialization */
    046    @Override
    047    public void init(Solver<Exam, ExamPlacement> solver) {
    048    }
    049
    050    /** Variable selection */
    051    @Override
    052    public Exam selectVariable(Solution<Exam, ExamPlacement> solution) {
    053        ExamModel model = (ExamModel) solution.getModel();
    054        if (model.nrUnassignedVariables() == 0)
    055            return null;
    056        if (iRandomSelection)
    057            return ToolBox.random(model.unassignedVariables());
    058        Exam variable = null;
    059        for (Exam v : model.unassignedVariables()) {
    060            if (variable == null || v.compareTo(variable) < 0)
    061                variable = v;
    062        }
    063        return variable;
    064    }
    065}