001package net.sf.cpsolver.exam.heuristics;
002
003import java.util.ArrayList;
004import java.util.Collection;
005import java.util.HashSet;
006import java.util.HashMap;
007import java.util.List;
008import java.util.Set;
009import java.util.TreeSet;
010
011import net.sf.cpsolver.exam.model.Exam;
012import net.sf.cpsolver.exam.model.ExamInstructor;
013import net.sf.cpsolver.exam.model.ExamModel;
014import net.sf.cpsolver.exam.model.ExamPeriodPlacement;
015import net.sf.cpsolver.exam.model.ExamPlacement;
016import net.sf.cpsolver.exam.model.ExamRoomPlacement;
017import net.sf.cpsolver.exam.model.ExamStudent;
018import net.sf.cpsolver.ifs.heuristics.NeighbourSelection;
019import net.sf.cpsolver.ifs.model.Neighbour;
020import net.sf.cpsolver.ifs.solution.Solution;
021import net.sf.cpsolver.ifs.solver.Solver;
022import net.sf.cpsolver.ifs.util.DataProperties;
023import net.sf.cpsolver.ifs.util.JProf;
024import net.sf.cpsolver.ifs.util.Progress;
025
026/**
027 * Examination timetabling construction heuristics based on graph vertex coloring.
028 * This approach is trying to find a (direct) conflict-free examination schedule using
029 * a depth-first search, assigning periods to exams in a way that there is not student or
030 * instructor direct conflict.
031 * <br>
032 * <br>
033 * This heuristics works in following modes (defined by Exam.ColoringConstructionMode).
034 * <ul>
035 * <li>Greedy .. all exams are greedily assigned with periods (and best available rooms);
036 *   Exams with smallest number of available periods (or highest number of connected exams
037 *   if multiple) are assigned first. 
038 * <li>ColorOnly .. all exams are assigned with periods using a depth-first search (ignoring
039 *   all other constraints), this coloring is then extended to exam placements as much as possible
040 * <li>Irredundant .. other constraints (distributions, rooms) are considered, however, to
041 *   speedup the search redundant colorings are avoided -- this may not find a complete solution,
042 *   especially when some periods are not swap-able
043 * <li>Full .. all constraints are considered, a complete solution is guaranteed to be found, if
044 *   it exists (and enough time is given)  
045 * </ul>
046 * <br>
047 * Time to run can  be limited using Exam.ColoringConstructionTimeLimit parameter (double precision,
048 * limit is in seconds, defaults to 5 minutes)
049 * <br>
050 * <br>
051 * 
052 * @version ExamTT 1.2 (Examination Timetabling)<br>
053 *          Copyright (C) 2008 - 2010 Tomáš Müller<br>
054 *          <a href="mailto:muller@unitime.org">muller@unitime.org</a><br>
055 *          <a href="http://muller.unitime.org">http://muller.unitime.org</a><br>
056 * <br>
057 *          This library is free software; you can redistribute it and/or modify
058 *          it under the terms of the GNU Lesser General Public License as
059 *          published by the Free Software Foundation; either version 3 of the
060 *          License, or (at your option) any later version. <br>
061 * <br>
062 *          This library is distributed in the hope that it will be useful, but
063 *          WITHOUT ANY WARRANTY; without even the implied warranty of
064 *          MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
065 *          Lesser General Public License for more details. <br>
066 * <br>
067 *          You should have received a copy of the GNU Lesser General Public
068 *          License along with this library; if not see
069 *          <a href='http://www.gnu.org/licenses/'>http://www.gnu.org/licenses/</a>.
070 */
071public class ExamColoringConstruction implements NeighbourSelection<Exam, ExamPlacement> {
072    private Progress iProgress;
073    private double iT0;
074    private double iTimeLimit = 300.0;
075    private boolean iTimeLimitReached = false;
076    private Solution<Exam, ExamPlacement> iSolution = null;
077    private Mode iMode = Mode.Full;
078    private Solver<Exam, ExamPlacement> iSolver;
079    
080    private static enum Mode {
081        Greedy(true, false, true),
082        ColorOnly(false, false, false),
083        Irredundant(false, false, false),
084        Full(false, true, true);
085        boolean iGreedy, iRedundant, iConstraintCheck;
086        private Mode(boolean gr, boolean r, boolean ch) { iGreedy = gr; iRedundant = r; iConstraintCheck = ch; }
087        public boolean isGreedy() { return iGreedy; }
088        public boolean isRedundant() { return iRedundant; }
089        public boolean isConstraintCheck() { return iConstraintCheck; } 
090    }
091    
092    public ExamColoringConstruction(DataProperties config) {
093        iTimeLimit = config.getPropertyDouble("Exam.ColoringConstructionTimeLimit", iTimeLimit);
094        iMode = Mode.valueOf(config.getProperty("Exam.ColoringConstructionMode", iMode.name()));
095    }
096    
097    private boolean backTrack(int index, HashSet<Integer> colorsUsedSoFar, Collection<Vertex> vertices) {
098        if (iTimeLimitReached || iSolver.isStop()) return false;
099        if (JProf.currentTimeSec() - iT0 > iTimeLimit) {
100            iTimeLimitReached = true;
101            return false;
102        }
103        if (index == vertices.size()) return true;
104        if (iProgress.getProgress() < index) {
105            iProgress.setProgress(index);
106            if (iMode.isConstraintCheck())
107                iSolution.saveBest();
108        }
109        Vertex vertex = null;
110        for (Vertex v: vertices) {
111            if (v.color() >= 0) continue;
112            if (vertex == null || v.compareTo(vertex) < 0) {
113                vertex = v;
114            }
115        }
116        if (colorsUsedSoFar != null) {
117            for (int color: new TreeSet<Integer>(colorsUsedSoFar))
118                if (vertex.colorize(color) && backTrack(1 + index, colorsUsedSoFar, vertices)) return true;
119            for (int color: vertex.domain()) {
120                if (colorsUsedSoFar.contains(color)) continue;
121                if (vertex.colorize(color)) {
122                    colorsUsedSoFar.add(color);
123                    if (backTrack(1 + index, colorsUsedSoFar, vertices)) return true;
124                    colorsUsedSoFar.remove(color);
125                }
126                break;
127            }
128        } else {
129            for (int color: vertex.domain())
130                if (vertex.colorize(color) && backTrack(1 + index, colorsUsedSoFar, vertices)) return true;
131        }
132        vertex.colorize(-1);
133        return false;
134    }
135
136    @Override
137    public void init(Solver<Exam, ExamPlacement> solver) {
138        iProgress = Progress.getInstance(solver.currentSolution().getModel());
139        iSolver = solver;
140    }
141    
142    public Set<ExamRoomPlacement> findRooms(Exam exam, ExamPeriodPlacement period) {
143        Set<ExamRoomPlacement> rooms = exam.findBestAvailableRooms(period);
144        if (rooms != null) return rooms;
145        
146        rooms = new HashSet<ExamRoomPlacement>();
147        int size = 0;
148        while (size < exam.getSize()) {
149            ExamRoomPlacement bestRoom = null; int bestSize = 0;
150            for (ExamRoomPlacement r: exam.getRoomPlacements()) {
151                if (!r.isAvailable(period.getPeriod())) continue;
152                if (rooms.contains(r)) continue;
153                if (!r.getRoom().getPlacements(period.getPeriod()).isEmpty()) continue;
154                int s = r.getSize(exam.hasAltSeating());
155                if (bestRoom == null || s > bestSize) {
156                    bestRoom = r;
157                    bestSize = s;
158                }
159            }
160            if (bestRoom == null) return rooms;
161            rooms.add(bestRoom); size += bestSize;
162        }
163        
164        return rooms;
165    }
166
167    @Override
168    public Neighbour<Exam, ExamPlacement> selectNeighbour(Solution<Exam, ExamPlacement> solution) {
169        iSolution = solution;
170        ExamModel model = (ExamModel)solution.getModel();
171        // if (!model.assignedVariables().isEmpty()) return null;
172        final HashMap<Exam, Vertex> vertices = new HashMap<Exam, Vertex>();
173        for (Exam x: model.variables()) {
174            vertices.put(x, new Vertex(x));
175        }
176        for (ExamStudent s: model.getStudents()) {
177            for (Exam x: s.variables()) {
178                for (Exam y: s.variables()) {
179                    if (!x.equals(y)) {
180                        vertices.get(x).neighbors().add(vertices.get(y));
181                        vertices.get(y).neighbors().add(vertices.get(x));
182                    }
183                }
184            }
185        }
186        for (ExamInstructor i: model.getInstructors()) {
187            for (Exam x: i.variables()) {
188                for (Exam y: i.variables()) {
189                    if (!x.equals(y)) {
190                        vertices.get(x).neighbors().add(vertices.get(y));
191                        vertices.get(y).neighbors().add(vertices.get(x));
192                    }
193                }
194            }
195        }
196        iProgress.setPhase("Graph coloring-based construction", vertices.size());
197        iProgress.info("Looking for a conflict-free assignment using " + model.getPeriods().size() + " periods.");
198        iT0 = JProf.currentTimeSec(); iTimeLimitReached = false;
199        if (iMode.isGreedy()) {
200            iProgress.info("Using greedy heuristics only (no backtracking)...");
201        } else if (backTrack(0, (iMode.isRedundant() ? null : new HashSet<Integer>()), vertices.values())) {
202            iProgress.info("Success!");
203        } else if (iTimeLimitReached) {
204            iProgress.info("There was no conflict-free schedule found during the given time.");
205        } else if (iSolver.isStop()) {
206            iProgress.info("Solver was stopped.");
207        } else {
208            if (iMode.isRedundant())
209                iProgress.info("There is no conflict-free schedule!");
210            else
211                iProgress.info("Conflict-free schedule not found.");
212        }
213        if (iMode.isConstraintCheck())
214            iSolution.restoreBest();
215        HashSet<Vertex> remaning = new HashSet<Vertex>();
216        for (Vertex v: vertices.values())
217            if (v.color() < 0) remaning.add(v);
218        remaining: while (!remaning.isEmpty()) {
219            Vertex vertex = null;
220            for (Vertex v: remaning)
221                if (vertex == null || v.compareTo(vertex) < 0)
222                    vertex = v;
223            remaning.remove(vertex);
224            for (int color: vertex.domain())
225                if (vertex.colorize(color)) continue remaining;
226        }
227        if (!iMode.isConstraintCheck()) {
228            return new Neighbour<Exam, ExamPlacement>() {
229                @Override
230                public void assign(long iteration) {
231                    iProgress.info("Using graph coloring solution ...");
232                    for (Vertex vertex: new TreeSet<Vertex>(vertices.values())) {
233                        ExamPeriodPlacement period = vertex.period();
234                        if (period == null || !vertex.exam().checkDistributionConstraints(period)) continue;
235                        Set<ExamRoomPlacement> rooms = findRooms(vertex.exam(), period);
236                        if (rooms == null) continue;
237                        vertex.exam().assign(iteration, new ExamPlacement(vertex.exam(), period, rooms));
238                    }
239                    HashSet<Vertex> unassigned = new HashSet<Vertex>();
240                    for (Vertex vertex: vertices.values()) {
241                        if (vertex.exam().getAssignment() == null) {
242                            unassigned.add(vertex);
243                            vertex.colorize(-1);
244                        }
245                    }
246                    iSolution.saveBest();
247                    iProgress.info("Extending ...");
248                    unassigned: while (!unassigned.isEmpty()) {
249                        Vertex vertex = null;
250                        for (Vertex v: unassigned)
251                            if (vertex == null || v.compareTo(vertex) < 0)
252                                vertex = v;
253                        unassigned.remove(vertex);
254                        for (int color: vertex.domain()) {
255                            if (!vertex.colorize(color)) continue;
256                            ExamPeriodPlacement period = vertex.period(color);
257                            if (period == null || !vertex.exam().checkDistributionConstraints(period)) continue;
258                            Set<ExamRoomPlacement> rooms = findRooms(vertex.exam(), period);
259                            if (rooms == null) continue;
260                            vertex.exam().assign(iteration, new ExamPlacement(vertex.exam(), period, rooms));
261                            continue unassigned;
262                        }
263                        vertex.colorize(-1);
264                    }
265                    iSolution.saveBest();
266                    iProgress.info("Construction done.");
267                }
268                @Override
269                public double value() {
270                    return 0;
271                }
272            };
273        }
274        return null;
275    }
276
277    /** Internal graph representation -- needed for domain caching */
278    private class Vertex implements Comparable<Vertex> {
279        private Exam iExam;
280        private List<Vertex> iNeighbors = new ArrayList<Vertex>();
281        private int iColor = -1;
282        private HashMap<Integer, ExamPeriodPlacement> iDomain = new HashMap<Integer, ExamPeriodPlacement>();
283        private HashMap<Integer, Vertex> iTaken = new HashMap<Integer, Vertex>();
284
285        public Vertex(Exam exam) {
286            iExam = exam;
287            for (ExamPeriodPlacement period: exam.getPeriodPlacements())
288                iDomain.put(period.getIndex(), period);
289        }
290        
291        public List<Vertex> neighbors() { return iNeighbors; }
292        
293        public Set<Integer> domain() { return iDomain.keySet(); }
294        
295        public ExamPeriodPlacement period() { return (iColor < 0 ? null : iDomain.get(iColor)); }
296        
297        public ExamPeriodPlacement period(int color) { return (color < 0 ? null : iDomain.get(color)); }
298
299        private boolean neighborColored(Vertex v, int color) {
300            if (!iDomain.containsKey(color)) return true;
301            if (iTaken.get(color) == null)
302                iTaken.put(color, v);
303            return iTaken.size() < iDomain.size();
304        }
305        
306        private void neighborUncolored(Vertex v, int color) {
307            if (!iDomain.containsKey(color)) return;
308            if (v.equals(iTaken.get(color))) {
309                for (Vertex w: neighbors()) {
310                    if (w.equals(v)) continue;
311                    if (w.color() == color) {
312                        iTaken.put(color, w);
313                        return;
314                    }
315                }
316                iTaken.remove(color);
317            }
318        }
319        
320        public int color() { return iColor; }
321        
322        public boolean colorize(int color) {
323            if (iColor == color) return true;
324            ExamPlacement placement = null;
325            if (color >= 0) {
326                if (iTaken.get(color) != null || !iDomain.containsKey(color))
327                    return false;
328                if (iMode.isConstraintCheck()) {
329                    ExamPeriodPlacement period = iDomain.get(color);
330                    if (!iExam.checkDistributionConstraints(period)) return false;
331                    Set<ExamRoomPlacement> rooms = findRooms(iExam, period);
332                    if (rooms == null) return false;
333                    placement = new ExamPlacement(iExam, period, rooms);
334                }
335            }
336            if (iColor >= 0) {
337                for (Vertex v: neighbors())
338                    v.neighborUncolored(this, iColor);
339            }
340            boolean success = true;
341            if (color >= 0) {
342                for (Vertex v: neighbors()) {
343                    if (!v.neighborColored(this, color)) {
344                        success = false; break;
345                    }
346                }
347            }
348            if (success) {
349                iColor = color;
350                if (iMode.isConstraintCheck()) {
351                    if (placement != null)
352                        iExam.assign(0l, placement);
353                    else
354                        iExam.unassign(0l);
355                }
356            } else { // undo
357                for (Vertex v: neighbors()) {
358                    v.neighborUncolored(this, color);
359                    if (iColor >= 0)
360                        v.neighborColored(this, iColor);
361                }
362            }
363            return success;
364        }
365        
366        public int degree() {
367            return iNeighbors.size();
368        }
369        
370        public int available() {
371            return iDomain.size() - iTaken.size();
372        }
373        
374        public int degreeNotColored() {
375            int ret = 0;
376            for (Vertex v: neighbors())
377                if (v.color() < 0) ret ++;
378            return ret;
379        }
380        
381        public Exam exam() { return iExam; }
382        
383        @Override
384        public int compareTo(Vertex v) {
385            if (available() < v.available()) return -1;
386            if (v.available() < available()) return 1;
387            if (degree() > v.degree()) return -1;
388            if (v.degree() > degree()) return 1;        
389            if (degreeNotColored() > v.degreeNotColored()) return -1;
390            if (v.degreeNotColored() > degreeNotColored()) return 1;
391            return Double.compare(exam().getId(), v.exam().getId());
392        }
393    }
394}