001package org.cpsolver.studentsct.heuristics.selection;
002
003import java.util.ArrayList;
004import java.util.Collections;
005import java.util.LinkedList;
006import java.util.List;
007import java.util.Queue;
008
009import org.cpsolver.ifs.heuristics.NeighbourSelection;
010import org.cpsolver.ifs.model.Neighbour;
011import org.cpsolver.ifs.solution.Solution;
012import org.cpsolver.ifs.solver.Solver;
013import org.cpsolver.ifs.util.DataProperties;
014import org.cpsolver.ifs.util.Progress;
015import org.cpsolver.studentsct.heuristics.RandomizedBacktrackNeighbourSelection;
016import org.cpsolver.studentsct.model.CourseRequest;
017import org.cpsolver.studentsct.model.Enrollment;
018import org.cpsolver.studentsct.model.FreeTimeRequest;
019import org.cpsolver.studentsct.model.Request;
020
021
022/**
023 * Use backtrack neighbour selection. For all unassigned variables (in a random
024 * order), {@link RandomizedBacktrackNeighbourSelection} is being used.
025 * 
026 * <br>
027 * <br>
028 * 
029 * @version StudentSct 1.3 (Student Sectioning)<br>
030 *          Copyright (C) 2007 - 2014 Tomas Muller<br>
031 *          <a href="mailto:muller@unitime.org">muller@unitime.org</a><br>
032 *          <a href="http://muller.unitime.org">http://muller.unitime.org</a><br>
033 * <br>
034 *          This library is free software; you can redistribute it and/or modify
035 *          it under the terms of the GNU Lesser General Public License as
036 *          published by the Free Software Foundation; either version 3 of the
037 *          License, or (at your option) any later version. <br>
038 * <br>
039 *          This library is distributed in the hope that it will be useful, but
040 *          WITHOUT ANY WARRANTY; without even the implied warranty of
041 *          MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
042 *          Lesser General Public License for more details. <br>
043 * <br>
044 *          You should have received a copy of the GNU Lesser General Public
045 *          License along with this library; if not see
046 *          <a href='http://www.gnu.org/licenses/'>http://www.gnu.org/licenses/</a>.
047 */
048
049public class BacktrackSelection implements NeighbourSelection<Request, Enrollment> {
050    private RandomizedBacktrackNeighbourSelection iRBtNSel = null;
051    protected Queue<Request> iRequests = null;
052    protected boolean iIncludeAssignedRequests = false;
053
054    public BacktrackSelection(DataProperties properties) {
055        iIncludeAssignedRequests = properties.getPropertyBoolean("Neighbour.IncludeAssignedRequests", iIncludeAssignedRequests);
056    }
057
058    public void init(Solver<Request, Enrollment> solver, String name) {
059        List<Request> variables = new ArrayList<Request>(iIncludeAssignedRequests ? solver.currentSolution().getModel().variables() : solver.currentSolution().getModel().unassignedVariables(solver.currentSolution().getAssignment()));
060        Collections.shuffle(variables);
061        iRequests = new LinkedList<Request>(variables);
062        if (iRBtNSel == null) {
063            try {
064                iRBtNSel = new RandomizedBacktrackNeighbourSelection(solver.getProperties());
065                iRBtNSel.init(solver);
066            } catch (Exception e) {
067                throw new RuntimeException(e.getMessage(), e);
068            }
069        }
070        Progress.getInstance(solver.currentSolution().getModel()).setPhase(name, variables.size());
071    }
072
073    @Override
074    public void init(Solver<Request, Enrollment> solver) {
075        init(solver, "Backtracking...");
076    }
077    
078    protected synchronized Request nextRequest() {
079        return iRequests.poll();
080    }
081
082    @Override
083    public Neighbour<Request, Enrollment> selectNeighbour(Solution<Request, Enrollment> solution) {
084        Request request = null;
085        while ((request = nextRequest()) != null) {
086            Progress.getInstance(solution.getModel()).incProgress();
087            Enrollment e = request.getAssignment(solution.getAssignment());
088            if (e != null && request instanceof FreeTimeRequest) continue;
089            if (e != null && e.getPriority() == 0 && ((CourseRequest)request).getSelectedChoices().isEmpty()) continue;
090            Neighbour<Request, Enrollment> n = iRBtNSel.selectNeighbour(solution, request);
091            if (n != null && n.value(solution.getAssignment()) <= 0.0)
092                return n;
093        }
094        return null;
095    }
096
097}