001package org.cpsolver.coursett.sectioning;
002
003import java.util.ArrayList;
004import java.util.Collection;
005import java.util.Iterator;
006import java.util.LinkedList;
007import java.util.List;
008import java.util.Queue;
009
010import org.cpsolver.coursett.model.Configuration;
011import org.cpsolver.coursett.model.Lecture;
012import org.cpsolver.coursett.model.Placement;
013import org.cpsolver.coursett.model.Student;
014import org.cpsolver.coursett.model.TimetableModel;
015import org.cpsolver.ifs.assignment.Assignment;
016import org.cpsolver.ifs.heuristics.NeighbourSelection;
017import org.cpsolver.ifs.model.Neighbour;
018import org.cpsolver.ifs.solution.Solution;
019import org.cpsolver.ifs.solver.Solver;
020import org.cpsolver.ifs.util.ToolBox;
021
022/**
023 * Generate student swaps. Rather than generating swaps at random, the class iterates between
024 * all classes and all conflicting students of each class and generate a random swap for
025 * each such student.
026 * 
027 * @version CourseTT 1.3 (University Course Timetabling)<br>
028 *          Copyright (C) 2017 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 */
046public class StudentSwapGenerator implements NeighbourSelection<Lecture, Placement> {
047    Iterator<Lecture> iLectures = null;
048    Lecture iLecture = null;
049    Iterator<Student> iStudents = null;
050    
051    @Override
052    public void init(Solver<Lecture, Placement> solver) {
053    }
054
055    @Override
056    public Neighbour<Lecture, Placement> selectNeighbour(Solution<Lecture, Placement> solution) {
057        TimetableModel model = (TimetableModel)solution.getModel();
058        if (model.getAllStudents().isEmpty()) return null;
059
060        boolean next = false;
061        while (iLecture == null || iStudents == null || !iStudents.hasNext()) {
062            if (iLectures == null || !iLectures.hasNext()) {
063                if (next) return null;
064                iLectures = model.variables().iterator();
065                next = true;
066            }
067            iLecture = iLectures.next();
068            if (iLecture.getConfiguration() == null || (iLecture.getConfiguration().getAltConfigurations().isEmpty() && iLecture.isSingleSection())) continue;
069            iStudents = iLecture.conflictStudents(solution.getAssignment()).iterator();
070        }
071        return generateSwap(model, solution.getAssignment(), iStudents.next(), iLecture.getConfiguration());
072    }
073    
074    public Neighbour<Lecture, Placement> selectNeighbour(Assignment<Lecture, Placement> assignment, Lecture lecture) {
075        return generateSwap((TimetableModel)lecture.getModel(), assignment, ToolBox.random(lecture.students()), lecture.getConfiguration());
076
077    }
078    
079    public Neighbour<Lecture, Placement> generateSwap(TimetableModel model, Assignment<Lecture, Placement> assignment, Student student, Configuration config) {
080        if (student == null || config == null) return null;
081        if (!config.getAltConfigurations().isEmpty()) {
082            int idx = ToolBox.random(config.getAltConfigurations().size() + 2);
083            if (idx > 1) config = config.getAltConfigurations().get(idx - 2);
084        }
085        Long subpartId = ToolBox.random(config.getTopSubpartIds());
086        int nrAttempts = ToolBox.random(10);
087        for (int i = 0; i < nrAttempts; i++) {
088            Lecture lecture = ToolBox.random(config.getTopLectures(subpartId));
089            Student other = ToolBox.random(lecture.students());
090            if (other != null && !student.equals(other)) {
091                StudentSwap swap = new StudentSwap(model, assignment, student, other, config.getOfferingId());
092                if (swap.isAllowed()) return swap;
093            }
094        }
095        List<Lecture> lectures = new ArrayList<Lecture>();
096        Queue<Collection<Lecture>> queue = new LinkedList<Collection<Lecture>>(config.getTopLectures().values());
097        while (!queue.isEmpty()) {
098            List<Lecture> adepts = new ArrayList<Lecture>();
099            for (Lecture adept: queue.poll())
100                if (student.canEnroll(adept)) adepts.add(adept);
101            if (adepts.isEmpty()) return null;
102            Lecture lect = ToolBox.random(adepts);
103            lectures.add(lect);
104            if (lect.hasAnyChildren())
105                queue.addAll(lect.getChildren().values());
106        }
107        StudentSwap swap = new StudentSwap(model, assignment, student, lectures);
108        return (swap.isAllowed() ? swap : null);
109    }
110
111}