001    package net.sf.cpsolver.studentsct.heuristics;
002    
003    import java.util.ArrayList;
004    import java.util.Iterator;
005    
006    import net.sf.cpsolver.ifs.heuristics.BacktrackNeighbourSelection;
007    import net.sf.cpsolver.ifs.util.DataProperties;
008    import net.sf.cpsolver.studentsct.model.CourseRequest;
009    import net.sf.cpsolver.studentsct.model.Enrollment;
010    import 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 Tomas Muller<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     */
057    public 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    }