001package net.sf.cpsolver.coursett.constraint;
002
003import java.util.ArrayList;
004import java.util.BitSet;
005import java.util.Collections;
006import java.util.HashMap;
007import java.util.List;
008import java.util.Map;
009import java.util.Set;
010import java.util.regex.Matcher;
011import java.util.regex.Pattern;
012
013import net.sf.cpsolver.coursett.Constants;
014import net.sf.cpsolver.coursett.model.Lecture;
015import net.sf.cpsolver.coursett.model.Placement;
016import net.sf.cpsolver.ifs.model.WeakeningConstraint;
017import net.sf.cpsolver.ifs.util.ToolBox;
018
019/**
020 * 
021 * The MaxBreaks constraint limits the number of blocks of non back-to-back classes of an instructor on a day.<br>
022 * It has two parameters: a maximal number of breaks and a minimal length of a break between two classes not to be considered in the same block.<br>
023 * Reference _MaxBreaks:1:30_ translates to a maximum number of one break (two blocks) on a day of classes not more than 30 minutes a part.<br>
024 * 
025 * @version CourseTT 1.2 (University Course Timetabling)<br>
026 *          Copyright (C) 2013 Tomáš Müller<br>
027 * <br>
028 *          This library is free software; you can redistribute it and/or modify
029 *          it under the terms of the GNU Lesser General Public License as
030 *          published by the Free Software Foundation; either version 3 of the
031 *          License, or (at your option) any later version. <br>
032 * <br>
033 *          This library is distributed in the hope that it will be useful, but
034 *          WITHOUT ANY WARRANTY; without even the implied warranty of
035 *          MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
036 *          Lesser General Public License for more details. <br>
037 * <br>
038 *          You should have received a copy of the GNU Lesser General Public
039 *          License along with this library; if not see
040 *          <a href='http://www.gnu.org/licenses/'>http://www.gnu.org/licenses/</a>.
041 */
042public class MaxBreaksFlexibleConstraint extends FlexibleConstraint implements WeakeningConstraint<Lecture, Placement> {
043    private int iMaxBreakBetweenBTB;
044    private int iMaxBlocksOnADay;
045    private Map<Lecture, Placement> iWeakAssignment = new HashMap<Lecture, Placement>();
046    
047    public MaxBreaksFlexibleConstraint(Long id, String owner, String preference, String reference) {
048        super(id, owner, preference, reference);     
049
050        Matcher matcher = Pattern.compile(FlexibleConstraintType.MAX_BREAKS.getPattern()).matcher(reference);
051        if (matcher.find()) {                
052            iMaxBlocksOnADay = 1 + Integer.parseInt(matcher.group(2));
053            iMaxBreakBetweenBTB = Integer.parseInt(matcher.group(3)) / Constants.SLOT_LENGTH_MIN;
054            iConstraintType = FlexibleConstraintType.MAX_BREAKS;           
055        }   
056    }
057
058    public List<Block> getBlocks(int dayCode, Set<Placement> conflicts, Placement value, HashMap<Lecture, Placement> assignments, BitSet week) {     
059        List<Placement> toBeSorted = new ArrayList<Placement>(getRelevantPlacements(dayCode, conflicts, value, assignments, week));
060        Collections.sort(toBeSorted, new PlacementTimeComparator());  
061        
062        return mergeToBlocks(toBeSorted, iMaxBreakBetweenBTB);
063    } 
064
065    @Override
066    public double getNrViolations(Set<Placement> conflicts, HashMap<Lecture, Placement> assignments) {
067        int penalty = 0;
068        // constraint is checked for every day in week
069        for (int dayCode : Constants.DAY_CODES) {
070            // constraint is checked for every week in semester (or for the whole semester)
071            for (BitSet week : getWeeks()) {
072                // each blocks contains placements which are BTB
073                List<Block> blocks = getBlocks(dayCode, null, null, assignments, week);
074                // too many blocks -> increase penalty
075                if (blocks.size() > iMaxBlocksOnADay)
076                    penalty += (blocks.size() - iMaxBlocksOnADay) * (blocks.size() - iMaxBlocksOnADay);
077            }
078        }
079        return penalty;
080    }
081
082    @Override
083    public void computeConflicts(Placement value, Set<Placement> conflicts) {
084        if (!isHard()) return;
085        
086        if (value.equals(iWeakAssignment.get(value.variable()))) {
087            for (Lecture v: variables())
088                if (v.getAssignment() == null && !v.equals(value.variable())) {
089                    // incomplete and week -- do not check for conflicts just yet
090                    return;
091                }
092        }
093        
094        // constraint is checked for every day in week
095        for (int dayCode : Constants.DAY_CODES) {
096            if ((value.getTimeLocation().getDayCode() & dayCode) == 0) continue; // ignore other days
097            // constraint is checked for every week in semester (or for the whole semester)
098            for (BitSet week : getWeeks()) {
099                if (week != null && !week.intersects(value.getTimeLocation().getWeekCode())) continue; // ignore other weeks
100                // each blocks contains placements which are BTB
101                List<Block> blocks = getBlocks(dayCode, conflicts, value, null, week);
102                while (blocks.size() > iMaxBlocksOnADay) {
103                    // too many blocks -> identify adepts for unassignment
104                    List<Block> adepts = new ArrayList<Block>(); int size = 0;
105                    for (Block block: blocks) {
106                        if (block.getPlacements().contains(value)) continue; // skip block containing given value
107                        // select adepts of the smallest size
108                        if (adepts.isEmpty() || size > block.getPlacements().size()) {
109                            adepts.clear();
110                            adepts.add(block);
111                            size = block.getPlacements().size();
112                        } else if (size == block.getPlacements().size()) {
113                            adepts.add(block);
114                        }
115                    }
116                    
117                    // pick one randomly
118                    Block block = ToolBox.random(adepts);
119                    blocks.remove(block);
120                    for (Placement conflict: block.getPlacements())
121                        if (conflict.equals(conflict.variable().getAssignment()))
122                            conflicts.add(conflict);
123                }
124            }
125        }
126    }
127
128    @Override
129    public void weaken() {
130    }
131
132    @Override
133    public void weaken(Placement value) {
134        if (isHard())
135            iWeakAssignment.put(value.variable(), value);
136    }
137    
138    @Override
139    public void assigned(long iteration, Placement value) {
140        super.assigned(iteration, value);
141        if (isHard())
142            iWeakAssignment.remove(value.variable());
143    }
144}