001package org.cpsolver.exam.heuristics;
002
003import org.cpsolver.exam.model.Exam;
004import org.cpsolver.exam.model.ExamModel;
005import org.cpsolver.exam.model.ExamPlacement;
006import org.cpsolver.ifs.assignment.Assignment;
007import org.cpsolver.ifs.heuristics.VariableSelection;
008import org.cpsolver.ifs.model.Variable;
009import org.cpsolver.ifs.solution.Solution;
010import org.cpsolver.ifs.solver.Solver;
011import org.cpsolver.ifs.util.DataProperties;
012import org.cpsolver.ifs.util.ToolBox;
013
014/**
015 * Unassigned variable selection. The "biggest" variable (using
016 * {@link Variable#compareTo(Variable)}) unassigned variable is selected. One is
017 * selected randomly if there are more than one of such variables.
018 * 
019 * @version ExamTT 1.3 (Examination Timetabling)<br>
020 *          Copyright (C) 2008 - 2014 Tomáš Müller<br>
021 *          <a href="mailto:muller@unitime.org">muller@unitime.org</a><br>
022 *          <a href="http://muller.unitime.org">http://muller.unitime.org</a><br>
023 * <br>
024 *          This library is free software; you can redistribute it and/or modify
025 *          it under the terms of the GNU Lesser General Public License as
026 *          published by the Free Software Foundation; either version 3 of the
027 *          License, or (at your option) any later version. <br>
028 * <br>
029 *          This library is distributed in the hope that it will be useful, but
030 *          WITHOUT ANY WARRANTY; without even the implied warranty of
031 *          MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
032 *          Lesser General Public License for more details. <br>
033 * <br>
034 *          You should have received a copy of the GNU Lesser General Public
035 *          License along with this library; if not see
036 *          <a href='http://www.gnu.org/licenses/'>http://www.gnu.org/licenses/</a>.
037 */
038public class ExamUnassignedVariableSelection implements VariableSelection<Exam, ExamPlacement> {
039    private boolean iRandomSelection = true;
040
041    /** Constructor 
042     * @param properties solver configuration
043     **/
044    public ExamUnassignedVariableSelection(DataProperties properties) {
045        iRandomSelection = properties.getPropertyBoolean("ExamUnassignedVariableSelection.random", iRandomSelection);
046    }
047
048    /** Initialization */
049    @Override
050    public void init(Solver<Exam, ExamPlacement> solver) {
051    }
052
053    /** Variable selection */
054    @Override
055    public Exam selectVariable(Solution<Exam, ExamPlacement> solution) {
056        ExamModel model = (ExamModel) solution.getModel();
057        Assignment<Exam, ExamPlacement> assignment = solution.getAssignment();
058        if (model.variables().size() == assignment.nrAssignedVariables())
059            return null;
060        if (iRandomSelection) {
061            int idx = ToolBox.random(model.variables().size() - assignment.nrAssignedVariables());
062            for (Exam v: model.variables()) {
063                if (assignment.getValue(v) != null) continue;
064                if (idx == 0) return v;
065                idx --;
066            }
067        }
068        Exam variable = null;
069        for (Exam v : model.variables()) {
070            if (assignment.getValue(v) != null) continue;
071            if (variable == null || v.compareTo(variable) < 0)
072                variable = v;
073        }
074        return variable;
075    }
076}