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 }