001package org.cpsolver.studentsct.heuristics;
002
003import java.util.ArrayList;
004import java.util.List;
005
006import org.cpsolver.ifs.heuristics.NeighbourSelection;
007import org.cpsolver.ifs.model.Neighbour;
008import org.cpsolver.ifs.solution.Solution;
009import org.cpsolver.ifs.solver.Solver;
010import org.cpsolver.ifs.util.DataProperties;
011import org.cpsolver.studentsct.StudentSectioningModel;
012import org.cpsolver.studentsct.model.Enrollment;
013import org.cpsolver.studentsct.model.Request;
014import org.cpsolver.studentsct.model.Student;
015
016
017/**
018 * Two-phase (Batch) student sectioning neighbour selection. It is based on
019 * {@link StudentSctNeighbourSelection}, however in the first round, only real
020 * students are sectioned. All dummy students are removed from the problem
021 * during initialization of this neighbour selection, they are returned into the
022 * problem after the first round of {@link StudentSctNeighbourSelection}.
023 * 
024 * <br>
025 * <br>
026 * 
027 * @author  Tomáš Müller
028 * @version StudentSct 1.3 (Student Sectioning)<br>
029 *          Copyright (C) 2007 - 2014 Tomáš Müller<br>
030 *          <a href="mailto:muller@unitime.org">muller@unitime.org</a><br>
031 *          <a href="http://muller.unitime.org">http://muller.unitime.org</a><br>
032 * <br>
033 *          This library is free software; you can redistribute it and/or modify
034 *          it under the terms of the GNU Lesser General Public License as
035 *          published by the Free Software Foundation; either version 3 of the
036 *          License, or (at your option) any later version. <br>
037 * <br>
038 *          This library is distributed in the hope that it will be useful, but
039 *          WITHOUT ANY WARRANTY; without even the implied warranty of
040 *          MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
041 *          Lesser General Public License for more details. <br>
042 * <br>
043 *          You should have received a copy of the GNU Lesser General Public
044 *          License along with this library; if not see
045 *          <a href='http://www.gnu.org/licenses/'>http://www.gnu.org/licenses/</a>.
046 */
047
048public class TwoPhaseStudentSctNeighbourSelection extends StudentSctNeighbourSelection {
049    private int iNrRounds = 7;
050
051    public TwoPhaseStudentSctNeighbourSelection(DataProperties properties) throws Exception {
052        super(properties);
053        iNrRounds = properties.getPropertyInt("TwoPhaseSectioning.NrRoundsFirstPhase", iNrRounds);
054    }
055
056    /** Initialization -- also remove all the dummy students from the problem */
057    @Override
058    public void init(Solver<Request, Enrollment> solver) {
059        super.init(solver);
060        if (removeDummyStudents(solver.currentSolution()))
061            registerSelection(new RestoreDummyStudents());
062    }
063
064    List<Student> iDummyStudents = null;
065
066    private boolean removeDummyStudents(Solution<Request, Enrollment> solution) {
067        StudentSectioningModel model = (StudentSectioningModel) solution.getModel();
068        if (model.getNrLastLikeStudents(false) == 0 || model.getNrRealStudents(false) == 0)
069            return false;
070        iDummyStudents = new ArrayList<Student>();
071        for (Student student : new ArrayList<Student>(model.getStudents())) {
072            if (student.isDummy()) {
073                iDummyStudents.add(student);
074                model.removeStudent(student);
075            }
076        }
077        return true;
078    }
079
080    private boolean addDummyStudents(Solution<Request, Enrollment> solution) {
081        if (iDummyStudents == null || iDummyStudents.isEmpty())
082            return false;
083        iNrRounds--;
084        if (iNrRounds > 0)
085            return false;
086        solution.restoreBest();
087        StudentSectioningModel model = (StudentSectioningModel) solution.getModel();
088        for (Student student : iDummyStudents) {
089            model.addStudent(student);
090        }
091        iDummyStudents = null;
092        solution.saveBest();
093        return true;
094    }
095
096    /**
097     * Return all dummy students into the problem, executed as the last phase of
098     * the first round
099     */
100    protected class RestoreDummyStudents implements NeighbourSelection<Request, Enrollment> {
101        public RestoreDummyStudents() {
102        }
103
104        @Override
105        public void init(Solver<Request, Enrollment> solver) {
106        }
107
108        /** Return all (removed) dummy students into the problem */
109        @Override
110        public Neighbour<Request, Enrollment> selectNeighbour(Solution<Request, Enrollment> solution) {
111            addDummyStudents(solution);
112            return null;
113        }
114    }
115}