001 package net.sf.cpsolver.studentsct.heuristics.selection;
002
003 import java.util.ArrayList;
004 import java.util.Collections;
005 import java.util.Iterator;
006 import java.util.List;
007
008 import net.sf.cpsolver.ifs.heuristics.NeighbourSelection;
009 import net.sf.cpsolver.ifs.model.Neighbour;
010 import net.sf.cpsolver.ifs.solution.Solution;
011 import net.sf.cpsolver.ifs.solver.Solver;
012 import net.sf.cpsolver.ifs.util.DataProperties;
013 import net.sf.cpsolver.ifs.util.Progress;
014 import net.sf.cpsolver.studentsct.heuristics.RandomizedBacktrackNeighbourSelection;
015 import net.sf.cpsolver.studentsct.model.Enrollment;
016 import net.sf.cpsolver.studentsct.model.Request;
017
018 /**
019 * Use backtrack neighbour selection. For all unassigned variables (in a random
020 * order), {@link RandomizedBacktrackNeighbourSelection} is being used.
021 *
022 * <br>
023 * <br>
024 *
025 * @version StudentSct 1.2 (Student Sectioning)<br>
026 * Copyright (C) 2007 - 2010 Tomas Muller<br>
027 * <a href="mailto:muller@unitime.org">muller@unitime.org</a><br>
028 * <a href="http://muller.unitime.org">http://muller.unitime.org</a><br>
029 * <br>
030 * This library is free software; you can redistribute it and/or modify
031 * it under the terms of the GNU Lesser General Public License as
032 * published by the Free Software Foundation; either version 3 of the
033 * License, or (at your option) any later version. <br>
034 * <br>
035 * This library is distributed in the hope that it will be useful, but
036 * WITHOUT ANY WARRANTY; without even the implied warranty of
037 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
038 * Lesser General Public License for more details. <br>
039 * <br>
040 * You should have received a copy of the GNU Lesser General Public
041 * License along with this library; if not see
042 * <a href='http://www.gnu.org/licenses/'>http://www.gnu.org/licenses/</a>.
043 */
044
045 public class BacktrackSelection implements NeighbourSelection<Request, Enrollment> {
046 private RandomizedBacktrackNeighbourSelection iRBtNSel = null;
047 private Iterator<Request> iRequestIterator = null;
048
049 public BacktrackSelection(DataProperties properties) {
050 }
051
052 public void init(Solver<Request, Enrollment> solver, String name) {
053 List<Request> unassigned = new ArrayList<Request>(solver.currentSolution().getModel().unassignedVariables());
054 Collections.shuffle(unassigned);
055 iRequestIterator = unassigned.iterator();
056 if (iRBtNSel == null) {
057 try {
058 iRBtNSel = new RandomizedBacktrackNeighbourSelection(solver.getProperties());
059 iRBtNSel.init(solver);
060 } catch (Exception e) {
061 throw new RuntimeException(e.getMessage(), e);
062 }
063 }
064 Progress.getInstance(solver.currentSolution().getModel()).setPhase(name, unassigned.size());
065 }
066
067 @Override
068 public void init(Solver<Request, Enrollment> solver) {
069 init(solver, "Backtracking...");
070 }
071
072 @Override
073 public Neighbour<Request, Enrollment> selectNeighbour(Solution<Request, Enrollment> solution) {
074 while (iRequestIterator.hasNext()) {
075 Request request = iRequestIterator.next();
076 Progress.getInstance(solution.getModel()).incProgress();
077 Neighbour<Request, Enrollment> n = iRBtNSel.selectNeighbour(solution, request);
078 if (n != null && n.value() <= 0.0)
079 return n;
080 }
081 return null;
082 }
083
084 }