    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}