Examination Timetabling: Availability

- when instructor or student direct conflicts are not allowed, also do not allow for availability violations

src/org/cpsolver/exam/heuristics/ExamConstruction.java

@@ -109,6 +109,10 @@ public Neighbour<Exam, ExamPlacement> checkLocalOptimality(Assignment<Exam, Exam
                         if (context.assignments().contains(exam.getId() + ":" + period.getIndex()))
                             continue;
                     }
+                    if (exam.countInstructorConflicts(assignment, period) > 0) {
+                        if (context.assignments().contains(exam.getId() + ":" + period.getIndex()))
+                            continue;
+                    }
                     if (!exam.checkDistributionConstraints(assignment, period))
                         continue;
                     ExamPlacement placement = new ExamPlacement(exam, period, null);
@@ -165,6 +169,10 @@ public Neighbour<Exam, ExamPlacement> selectNeighbour(Solution<Exam, ExamPlaceme
                 if (context.assignments().contains(bestExam.getId() + ":" + period.getIndex()))
                     continue;
             }
+            if (bestExam.countInstructorConflicts(assignment, period) > 0) {
+                if (context.assignments().contains(bestExam.getId() + ":" + period.getIndex()))
+                    continue;
+            }
             if (!bestExam.checkDistributionConstraints(assignment, period))
                 continue;
             ExamPlacement placement = new ExamPlacement(bestExam, period, null);

src/org/cpsolver/exam/model/Exam.java

@@ -94,6 +94,7 @@ public class Exam extends Variable<Exam, ExamPlacement> {
 
     private ArrayList<ExamOwner> iOwners = new ArrayList<ExamOwner>();
     private List<ExamPeriodPlacement> iPeriodPlacements = null;
+    private List<ExamPeriodPlacement> iAvailablePeriodPlacements = null;
     private List<ExamRoomPlacement> iRoomPlacements = null;
     private List<ExamRoomPlacement> iRoomPreferredPlacements = null;
 
@@ -250,9 +251,23 @@ public synchronized List<ExamRoomPlacement> getPreferredRoomPlacements() {
      * @return list of {@link ExamPeriodPlacement}
      */
     public List<ExamPeriodPlacement> getPeriodPlacements() {
-        return iPeriodPlacements;
+        if (iAvailablePeriodPlacements == null) {
+            iAvailablePeriodPlacements = new ArrayList<ExamPeriodPlacement>(iPeriodPlacements.size());
+            for (ExamPeriodPlacement p: iPeriodPlacements) {
+                boolean available = true;
+                for (ExamInstructor i: getInstructors())
+                    if (!i.isAllowDirectConflicts() && !i.isAvailable(p.getPeriod())) { available = false; break; }
+                for (ExamStudent s: getStudents())
+                    if (!s.isAllowDirectConflicts() && !s.isAvailable(p.getPeriod())) { available = false; break; }
+                if (available)
+                    iAvailablePeriodPlacements.add(p);
+            }
+            if (iAvailablePeriodPlacements.isEmpty())
+                sLog.error("  Exam " + getName() + " has no available periods.");
+        }
+        return iAvailablePeriodPlacements;
     }
-
+    
     /**
      * Initialize exam's domain.
      */
@@ -466,6 +481,7 @@ public void addContstraint(Constraint<Exam, ExamPlacement> constraint) {
         if (constraint instanceof ExamInstructor)
             iInstructors.add((ExamInstructor) constraint);
         super.addContstraint(constraint);
+        iAvailablePeriodPlacements = null;
     }
 
     /**
@@ -485,6 +501,7 @@ public void removeContstraint(Constraint<Exam, ExamPlacement> constraint) {
         if (constraint instanceof ExamInstructor)
             iInstructors.remove(constraint);
         super.removeContstraint(constraint);
+        iAvailablePeriodPlacements = null;
     }
 
     /**
@@ -932,6 +949,29 @@ public int countStudentConflicts(Assignment<Exam, ExamPlacement> assignment, Exa
         }
         return conf;
     }
+
+    /**
+     * Number of instructor of this exam (that does not have direct conflicts
+     * allowed, see {@link ExamInstructor#canConflict(Exam, Exam)}) that attend
+     * some other exam in the given period.
+     * 
+     * @param assignment current assignment
+     * @param period
+     *            a period
+     * @return number of direct student conflicts that are prohibited
+     */
+    public int countInstructorConflicts(Assignment<Exam, ExamPlacement> assignment, ExamPeriodPlacement period) {
+        int conf = 0;
+        Map<ExamInstructor, Set<Exam>> instructorsOfPeriod = ((ExamModel)getModel()).getInstructorsOfPeriod(assignment, period.getPeriod());
+        for (ExamInstructor i : getInstructors()) {
+            Set<Exam> exams = instructorsOfPeriod.get(i);
+            if (exams == null) continue;
+            for (Exam exam : exams) {
+                if (!exam.equals(this) && !i.canConflict(this, exam)) conf++;
+            }
+        }
+        return conf;
+    }
 
     /**
      * List of exams that are assigned to the given period and share one or more
@@ -1092,7 +1132,7 @@ public Collection<ExamOwner> getOwners(ExamInstructor instructor) {
      * @return the appropriate period placement
      */
     public ExamPeriodPlacement getPeriodPlacement(Long periodId) {
-        for (ExamPeriodPlacement periodPlacement : iPeriodPlacements) {
+        for (ExamPeriodPlacement periodPlacement : getPeriodPlacements()) {
             if (periodPlacement.getId().equals(periodId))
                 return periodPlacement;
         }

src/org/cpsolver/exam/model/ExamInstructor.java

@@ -238,6 +238,21 @@ public void setAvailable(int period, boolean available) {
         iAvailable[period] = available;
     }
 
+    /**
+     * True if the given two exams can have a direct instructor conflict with this
+     * instructor, i.e., they can be placed at the same period.
+     * 
+     * @param ex1
+     *            an exam
+     * @param ex2
+     *            an exam
+     * @return {@link ExamStudent#isAllowDirectConflicts()} and
+     *         {@link Exam#isAllowDirectConflicts()} for both exams
+     */
+    public boolean canConflict(Exam ex1, Exam ex2) {
+        return isAllowDirectConflicts() && ex1.isAllowDirectConflicts() && ex2.isAllowDirectConflicts();
+    }
+
     /*
     @Override
     public Context createAssignmentContext(Assignment<Exam, ExamPlacement> assignment) {