    001package net.sf.cpsolver.studentsct.heuristics;
    002
    003import java.util.ArrayList;
    004import java.util.List;
    005
    006import net.sf.cpsolver.ifs.heuristics.NeighbourSelection;
    007import net.sf.cpsolver.ifs.model.Neighbour;
    008import net.sf.cpsolver.ifs.solution.Solution;
    009import net.sf.cpsolver.ifs.solver.Solver;
    010import net.sf.cpsolver.ifs.util.DataProperties;
    011import net.sf.cpsolver.studentsct.StudentSectioningModel;
    012import net.sf.cpsolver.studentsct.model.Enrollment;
    013import net.sf.cpsolver.studentsct.model.Request;
    014import net.sf.cpsolver.studentsct.model.Student;
    015
    016/**
    017 * Two-phase (Batch) student sectioning neighbour selection. It is based on
    018 * {@link StudentSctNeighbourSelection}, however in the first round, only real
    019 * students are sectioned. All dummy students are removed from the problem
    020 * during initialization of this neighbour selection, they are returned into the
    021 * problem after the first round of {@link StudentSctNeighbourSelection}.
    022 *
    023 * <br>
    024 * <br>
    025 *
    026 * @version StudentSct 1.2 (Student Sectioning)<br>
    027 *          Copyright (C) 2007 - 2010 Tomáš Müller<br>
    028 *          <a href="mailto:muller@unitime.org">muller@unitime.org</a><br>
    029 *          <a href="http://muller.unitime.org">http://muller.unitime.org</a><br>
    030 * <br>
    031 *          This library is free software; you can redistribute it and/or modify
    032 *          it under the terms of the GNU Lesser General Public License as
    033 *          published by the Free Software Foundation; either version 3 of the
    034 *          License, or (at your option) any later version. <br>
    035 * <br>
    036 *          This library is distributed in the hope that it will be useful, but
    037 *          WITHOUT ANY WARRANTY; without even the implied warranty of
    038 *          MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
    039 *          Lesser General Public License for more details. <br>
    040 * <br>
    041 *          You should have received a copy of the GNU Lesser General Public
    042 *          License along with this library; if not see
    043 *          <a href='http://www.gnu.org/licenses/'>http://www.gnu.org/licenses/</a>.
    044 */
    045
    046public class TwoPhaseStudentSctNeighbourSelection extends StudentSctNeighbourSelection {
    047    private int iNrRounds = 7;
    048
    049    public TwoPhaseStudentSctNeighbourSelection(DataProperties properties) throws Exception {
    050        super(properties);
    051        iNrRounds = properties.getPropertyInt("TwoPhaseSectioning.NrRoundsFirstPhase", iNrRounds);
    052    }
    053
    054    /** Initialization -- also remove all the dummy students from the problem */
    055    @Override
    056    public void init(Solver<Request, Enrollment> solver) {
    057        super.init(solver);
    058        if (removeDummyStudents(solver.currentSolution()))
    059            registerSelection(new RestoreDummyStudents());
    060    }
    061
    062    List<Student> iDummyStudents = null;
    063
    064    private boolean removeDummyStudents(Solution<Request, Enrollment> solution) {
    065        StudentSectioningModel model = (StudentSectioningModel) solution.getModel();
    066        if (model.getNrLastLikeStudents(false) == 0 || model.getNrRealStudents(false) == 0)
    067            return false;
    068        iDummyStudents = new ArrayList<Student>();
    069        for (Student student : new ArrayList<Student>(model.getStudents())) {
    070            if (student.isDummy()) {
    071                iDummyStudents.add(student);
    072                model.removeStudent(student);
    073            }
    074        }
    075        return true;
    076    }
    077
    078    private boolean addDummyStudents(Solution<Request, Enrollment> solution) {
    079        if (iDummyStudents == null || iDummyStudents.isEmpty())
    080            return false;
    081        iNrRounds--;
    082        if (iNrRounds > 0)
    083            return false;
    084        solution.restoreBest();
    085        StudentSectioningModel model = (StudentSectioningModel) solution.getModel();
    086        for (Student student : iDummyStudents) {
    087            model.addStudent(student);
    088        }
    089        iDummyStudents = null;
    090        solution.saveBest();
    091        return true;
    092    }
    093
    094    /**
    095     * Return all dummy students into the problem, executed as the last phase of
    096     * the first round
    097     */
    098    protected class RestoreDummyStudents implements NeighbourSelection<Request, Enrollment> {
    099        public RestoreDummyStudents() {
    100        }
    101
    102        @Override
    103        public void init(Solver<Request, Enrollment> solver) {
    104        }
    105
    106        /** Return all (removed) dummy students into the problem */
    107        @Override
    108        public Neighbour<Request, Enrollment> selectNeighbour(Solution<Request, Enrollment> solution) {
    109            addDummyStudents(solution);
    110            return null;
    111        }
    112    }
    113}