001    package net.sf.cpsolver.exam.heuristics;
002    
003    import net.sf.cpsolver.exam.model.Exam;
004    import net.sf.cpsolver.exam.model.ExamModel;
005    import net.sf.cpsolver.exam.model.ExamPlacement;
006    import net.sf.cpsolver.ifs.heuristics.VariableSelection;
007    import net.sf.cpsolver.ifs.model.Variable;
008    import net.sf.cpsolver.ifs.solution.Solution;
009    import net.sf.cpsolver.ifs.solver.Solver;
010    import net.sf.cpsolver.ifs.util.DataProperties;
011    import 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 Tomas Muller<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     */
037    public 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    }