001package net.sf.cpsolver.studentsct.heuristics.selection;
002
003import java.util.ArrayList;
004import java.util.Collections;
005import java.util.Iterator;
006import java.util.List;
007
008import net.sf.cpsolver.ifs.heuristics.NeighbourSelection;
009import net.sf.cpsolver.ifs.model.Neighbour;
010import net.sf.cpsolver.ifs.solution.Solution;
011import net.sf.cpsolver.ifs.solver.Solver;
012import net.sf.cpsolver.ifs.util.DataProperties;
013import net.sf.cpsolver.ifs.util.Progress;
014import net.sf.cpsolver.studentsct.heuristics.RandomizedBacktrackNeighbourSelection;
015import net.sf.cpsolver.studentsct.model.Enrollment;
016import 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 Tomáš Müller<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
045public 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}