    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}