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}