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