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 * @author  Tomáš Müller
020 * @version ExamTT 1.3 (Examination Timetabling)<br>
021 *          Copyright (C) 2008 - 2014 Tomáš Müller<br>
022 *          <a href="mailto:muller@unitime.org">muller@unitime.org</a><br>
023 *          <a href="http://muller.unitime.org">http://muller.unitime.org</a><br>
024 * <br>
025 *          This library is free software; you can redistribute it and/or modify
026 *          it under the terms of the GNU Lesser General Public License as
027 *          published by the Free Software Foundation; either version 3 of the
028 *          License, or (at your option) any later version. <br>
029 * <br>
030 *          This library is distributed in the hope that it will be useful, but
031 *          WITHOUT ANY WARRANTY; without even the implied warranty of
032 *          MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
033 *          Lesser General Public License for more details. <br>
034 * <br>
035 *          You should have received a copy of the GNU Lesser General Public
036 *          License along with this library; if not see
037 *          <a href='http://www.gnu.org/licenses/'>http://www.gnu.org/licenses/</a>.
038 */
039public class ExamUnassignedVariableSelection implements VariableSelection<Exam, ExamPlacement> {
040    private boolean iRandomSelection = true;
041
042    /** Constructor 
043     * @param properties solver configuration
044     **/
045    public ExamUnassignedVariableSelection(DataProperties properties) {
046        iRandomSelection = properties.getPropertyBoolean("ExamUnassignedVariableSelection.random", iRandomSelection);
047    }
048
049    /** Initialization */
050    @Override
051    public void init(Solver<Exam, ExamPlacement> solver) {
052    }
053
054    /** Variable selection */
055    @Override
056    public Exam selectVariable(Solution<Exam, ExamPlacement> solution) {
057        ExamModel model = (ExamModel) solution.getModel();
058        Assignment<Exam, ExamPlacement> assignment = solution.getAssignment();
059        if (model.variables().size() == assignment.nrAssignedVariables())
060            return null;
061        if (iRandomSelection) {
062            int idx = ToolBox.random(model.variables().size() - assignment.nrAssignedVariables());
063            for (Exam v: model.variables()) {
064                if (assignment.getValue(v) != null) continue;
065                if (idx == 0) return v;
066                idx --;
067            }
068        }
069        Exam variable = null;
070        for (Exam v : model.variables()) {
071            if (assignment.getValue(v) != null) continue;
072            if (variable == null || v.compareTo(variable) < 0)
073                variable = v;
074        }
075        return variable;
076    }
077}