001package net.sf.cpsolver.studentsct.heuristics;
002
003import java.util.ArrayList;
004import java.util.Iterator;
005
006import net.sf.cpsolver.ifs.heuristics.BacktrackNeighbourSelection;
007import net.sf.cpsolver.ifs.util.DataProperties;
008import net.sf.cpsolver.studentsct.model.CourseRequest;
009import net.sf.cpsolver.studentsct.model.Enrollment;
010import net.sf.cpsolver.studentsct.model.Request;
011
012/**
013 * Randomized backtracking-based neighbour selection. This class extends
014 * {@link RandomizedBacktrackNeighbourSelection}, however, only a randomly
015 * selected subset of enrollments of each request is considered (
016 * {@link CourseRequest#computeRandomEnrollments(int)} with the given limit is
017 * used).
018 * 
019 * <br>
020 * <br>
021 * Parameters: <br>
022 * <table border='1'>
023 * <tr>
024 * <th>Parameter</th>
025 * <th>Type</th>
026 * <th>Comment</th>
027 * </tr>
028 * <tr>
029 * <td>Neighbour.MaxValues</td>
030 * <td>{@link Integer}</td>
031 * <td>Limit on the number of enrollments to be visited of each
032 * {@link CourseRequest}.</td>
033 * </tr>
034 * </table>
035 * <br>
036 * <br>
037 * 
038 * @version StudentSct 1.2 (Student Sectioning)<br>
039 *          Copyright (C) 2007 - 2010 Tomáš Müller<br>
040 *          <a href="mailto:muller@unitime.org">muller@unitime.org</a><br>
041 *          <a href="http://muller.unitime.org">http://muller.unitime.org</a><br>
042 * <br>
043 *          This library is free software; you can redistribute it and/or modify
044 *          it under the terms of the GNU Lesser General Public License as
045 *          published by the Free Software Foundation; either version 3 of the
046 *          License, or (at your option) any later version. <br>
047 * <br>
048 *          This library is distributed in the hope that it will be useful, but
049 *          WITHOUT ANY WARRANTY; without even the implied warranty of
050 *          MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
051 *          Lesser General Public License for more details. <br>
052 * <br>
053 *          You should have received a copy of the GNU Lesser General Public
054 *          License along with this library; if not see
055 *          <a href='http://www.gnu.org/licenses/'>http://www.gnu.org/licenses/</a>.
056 */
057public class RandomizedBacktrackNeighbourSelection extends BacktrackNeighbourSelection<Request, Enrollment> {
058    private int iMaxValues = 100;
059
060    /**
061     * Constructor
062     * 
063     * @param properties
064     *            configuration
065     * @throws Exception
066     */
067    public RandomizedBacktrackNeighbourSelection(DataProperties properties) throws Exception {
068        super(properties);
069        iMaxValues = properties.getPropertyInt("Neighbour.MaxValues", iMaxValues);
070    }
071
072    /**
073     * List of values of a variable.
074     * {@link CourseRequest#computeRandomEnrollments(int)} with the provided
075     * limit is used for a {@link CourseRequest}.
076     */
077    @Override
078    protected Iterator<Enrollment> values(Request variable) {
079        if (iMaxValues > 0 && variable instanceof CourseRequest) {
080            return new ArrayList<Enrollment>(((CourseRequest) variable).computeRandomEnrollments(iMaxValues))
081                    .iterator();
082        }
083        return variable.values().iterator();
084    }
085}