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