001package org.cpsolver.studentsct.heuristics.selection;
002
003import java.text.DecimalFormat;
004import java.util.ArrayList;
005import java.util.Collection;
006import java.util.Collections;
007import java.util.Comparator;
008import java.util.ConcurrentModificationException;
009import java.util.LinkedList;
010import java.util.List;
011import java.util.ListIterator;
012import java.util.Map;
013
014import org.cpsolver.ifs.assignment.Assignment;
015import org.cpsolver.ifs.heuristics.BacktrackNeighbourSelection;
016import org.cpsolver.ifs.heuristics.NeighbourSelection;
017import org.cpsolver.ifs.model.InfoProvider;
018import org.cpsolver.ifs.model.Neighbour;
019import org.cpsolver.ifs.solution.Solution;
020import org.cpsolver.ifs.solver.Solver;
021import org.cpsolver.ifs.solver.SolverListener;
022import org.cpsolver.ifs.util.DataProperties;
023import org.cpsolver.ifs.util.Progress;
024import org.cpsolver.studentsct.filter.StudentFilter;
025import org.cpsolver.studentsct.heuristics.RandomizedBacktrackNeighbourSelection;
026import org.cpsolver.studentsct.model.CourseRequest;
027import org.cpsolver.studentsct.model.Enrollment;
028import org.cpsolver.studentsct.model.FreeTimeRequest;
029import org.cpsolver.studentsct.model.Request;
030import org.cpsolver.studentsct.model.Request.RequestPriority;
031import org.cpsolver.studentsct.model.Student.StudentPriority;
032
033
034/**
035 * Use backtrack neighbour selection. For all unassigned variables (in a random
036 * order), {@link RandomizedBacktrackNeighbourSelection} is being used.
037 * 
038 * <br>
039 * <br>
040 * 
041 * @author  Tomáš Müller
042 * @version StudentSct 1.3 (Student Sectioning)<br>
043 *          Copyright (C) 2007 - 2014 Tomáš Müller<br>
044 *          <a href="mailto:muller@unitime.org">muller@unitime.org</a><br>
045 *          <a href="http://muller.unitime.org">http://muller.unitime.org</a><br>
046 * <br>
047 *          This library is free software; you can redistribute it and/or modify
048 *          it under the terms of the GNU Lesser General Public License as
049 *          published by the Free Software Foundation; either version 3 of the
050 *          License, or (at your option) any later version. <br>
051 * <br>
052 *          This library is distributed in the hope that it will be useful, but
053 *          WITHOUT ANY WARRANTY; without even the implied warranty of
054 *          MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
055 *          Lesser General Public License for more details. <br>
056 * <br>
057 *          You should have received a copy of the GNU Lesser General Public
058 *          License along with this library; if not see
059 *          <a href='http://www.gnu.org/licenses/'>http://www.gnu.org/licenses/</a>.
060 */
061
062public class BacktrackSelection implements NeighbourSelection<Request, Enrollment>, InfoProvider<Request, Enrollment>, SolverListener<Request, Enrollment> {
063    private static DecimalFormat sDF = new DecimalFormat("0.00");
064    protected RandomizedBacktrackNeighbourSelection iRBtNSel = null;
065    protected LinkedList<Request> iRequests = null;
066    protected boolean iIncludeAssignedRequests = false;
067    
068    protected long iNbrIterations = 0;
069    protected long iMaxIterations = 0;
070    protected long iTotalTime = 0;
071    protected long iNbrTimeoutReached = 0;
072    protected long iNbrNoSolution = 0;
073    protected StudentFilter iFilter = null;
074    protected RequestComparator iRequestComparator = null;
075
076    public BacktrackSelection(DataProperties properties) {
077        iIncludeAssignedRequests = properties.getPropertyBoolean("Neighbour.IncludeAssignedRequests", iIncludeAssignedRequests);
078        iRequestComparator = new RequestComparator(properties);
079    }
080
081    public void init(Solver<Request, Enrollment> solver, String name) {
082        List<Request> variables = new ArrayList<Request>(iIncludeAssignedRequests ? solver.currentSolution().getModel().variables() : solver.currentSolution().getModel().unassignedVariables(solver.currentSolution().getAssignment()));
083        Collections.shuffle(variables);
084        Collections.sort(variables, iRequestComparator);
085        iRequests = new LinkedList<Request>(variables);
086        if (iRBtNSel == null) {
087            try {
088                iRBtNSel = new RandomizedBacktrackNeighbourSelection(solver.getProperties());
089                iRBtNSel.init(solver);
090            } catch (Exception e) {
091                throw new RuntimeException(e.getMessage(), e);
092            }
093        }
094        Progress.getInstance(solver.currentSolution().getModel()).setPhase(name, variables.size());
095    }
096
097    @Override
098    public void init(Solver<Request, Enrollment> solver) {
099        init(solver, "Backtracking" + (iFilter == null ? "" : " (" + iFilter.getName().toLowerCase() + " students)") + "...");
100        
101        iNbrIterations = 0;
102        iNbrTimeoutReached = 0;
103        iNbrNoSolution = 0;
104        iTotalTime = 0;
105        iMaxIterations = Math.max(10,  2 * iRequests.size());
106    }
107    
108    protected synchronized Request nextRequest() {
109        while (true) {
110            Request request = iRequests.poll();
111            if (request == null) return null;
112            if (iFilter == null || iFilter.accept(request.getStudent())) return request;
113        }
114    }
115    
116    public synchronized void addRequest(Request request) {
117        if (iRequests != null && request != null && !request.getStudent().isDummy()) {
118            if (request.getStudent().getPriority().ordinal() < StudentPriority.Normal.ordinal() || request.getRequestPriority().ordinal() < RequestPriority.Normal.ordinal()) {
119                for (ListIterator<Request> i = iRequests.listIterator(); i.hasNext();) {
120                    Request r = i.next();
121                    if (iRequestComparator.compare(r, request) > 0) {
122                        i.previous(); // go one back
123                        i.add(request);
124                        return;
125                    }
126                }
127            }
128            iRequests.add(request);
129        }
130    }
131
132    @Override
133    public Neighbour<Request, Enrollment> selectNeighbour(Solution<Request, Enrollment> solution) {
134        Request request = null;
135        if (iNbrIterations > iMaxIterations) return null;
136        while ((request = nextRequest()) != null) {
137            Progress.getInstance(solution.getModel()).incProgress();
138            Enrollment e = request.getAssignment(solution.getAssignment());
139            if (e != null && request instanceof FreeTimeRequest) continue;
140            if (e != null && e.getPriority() == 0 && ((CourseRequest)request).getSelectedChoices().isEmpty()) continue;
141            for (int i = 0; i < 5; i++) {
142                try {
143                    Neighbour<Request, Enrollment> n = iRBtNSel.selectNeighbour(solution, request);
144                    if (iRBtNSel.getContext() != null) {
145                        iNbrIterations ++;
146                        iTotalTime += iRBtNSel.getContext().getTime();
147                        if (iRBtNSel.getContext().isTimeoutReached()) iNbrTimeoutReached ++;
148                        if (n == null) iNbrNoSolution ++;
149                    }
150                    if (n != null && n.value(solution.getAssignment()) <= 0.0)
151                        return n;
152                    break;
153                } catch (ConcurrentModificationException ex) {}
154            }
155        }
156        return null;
157    }
158
159    @Override
160    public void getInfo(Assignment<Request, Enrollment> assignment, Map<String, String> info) {
161        if (iNbrIterations > 0)
162            info.put("Timing of " + getClass().getSimpleName(), sDF.format(((double)iTotalTime) / iNbrIterations) + " ms/it (" +
163                    iNbrIterations + " iterations, " +
164                    (iNbrNoSolution == 0 ? "" : sDF.format(100.0 * iNbrNoSolution / iNbrIterations) + "% no solution, ") +
165                    sDF.format(100.0 * iNbrTimeoutReached / iNbrIterations) + "% time limit of " + sDF.format(iRBtNSel.getTimeout() / 1000.0) + " seconds reached" +
166                    (iNbrIterations > iMaxIterations ? ", stopped after " + iNbrIterations + " iterations" : "") +
167                    ")");
168    }
169
170    @Override
171    public void getInfo(Assignment<Request, Enrollment> assignment, Map<String, String> info, Collection<Request> variables) {
172    }
173    
174    /**
175     * Only consider students meeting the given filter.
176     */
177    public StudentFilter getFilter() { return iFilter; }
178    
179    /**
180     * Only consider students meeting the given filter.
181     */
182    public BacktrackSelection withFilter(StudentFilter filter) { iFilter = filter; return this; }
183    
184    @Override
185    public boolean variableSelected(Assignment<Request, Enrollment> assignment, long iteration, Request variable) {
186        return false;
187    }
188    @Override
189    public boolean valueSelected(Assignment<Request, Enrollment> assignment, long iteration, Request variable, Enrollment value) {
190        return false;
191    }
192    @Override
193    public boolean neighbourSelected(Assignment<Request, Enrollment> assignment, long iteration, Neighbour<Request, Enrollment> neighbour) {
194        return false;
195    }
196    @Override
197    public void neighbourFailed(Assignment<Request, Enrollment> assignment, long iteration, Neighbour<Request, Enrollment> neighbour) {
198        if (neighbour instanceof BacktrackNeighbourSelection.BackTrackNeighbour)
199            addRequest(((BacktrackNeighbourSelection<Request, Enrollment>.BackTrackNeighbour)neighbour).getAssignments().get(0).getRequest());
200    }
201    
202    public static class RequestComparator implements Comparator<Request> {
203        protected boolean iPreferPriorityStudents = true;
204        protected RequestComparator(DataProperties properties) {
205            iPreferPriorityStudents = properties.getPropertyBoolean("Sectioning.PriorityStudentsFirstSelection.AllIn", true);
206        }
207        
208        @Override
209        public int compare(Request r1, Request r2) {
210            if (iPreferPriorityStudents) {
211                if (r1.getStudent().getPriority() != r2.getStudent().getPriority())
212                    return r1.getStudent().getPriority().compareTo(r2.getStudent().getPriority());
213                if (r1.getRequestPriority() != r2.getRequestPriority())
214                    return r1.getRequestPriority().compareTo(r2.getRequestPriority());
215            } else {
216                if (r1.getRequestPriority() != r2.getRequestPriority())
217                    return r1.getRequestPriority().compareTo(r2.getRequestPriority());
218                if (r1.getRequestPriority() != r2.getRequestPriority())
219                    return r1.getStudent().getPriority().compareTo(r2.getStudent().getPriority());
220            }
221            if (r1.isAlternative() != r2.isAlternative())
222                return r2.isAlternative() ? -1 : 1; 
223            if (r1.getPriority() != r2.getPriority())
224                return r1.getPriority() < r2.getPriority() ? -1 : 1;
225            return 0;
226        }
227    }
228}