impl: ldp find gaps fitting

assignment/src/main/java/appointmentplanner/LocalDayPlanImpl.java

@@ -89,10 +89,32 @@ public class LocalDayPlanImpl implements LocalDayPlan {
     throw new UnsupportedOperationException("Unimplemented method 'findMatchingFreeSlotsOfDuration'");
   }
 
+  private CustomLinkedList<TimeSlot> traverseGapsFitting(Duration toFind, CustomLinkedList<TimeSlot> goodSlots,
+      Instant startOfBefore, Iterator<Appointment> iterator) {
+
+    boolean hasNext = iterator.hasNext();
+
+    Appointment nextAppointment = hasNext ? iterator.next() : null;
+
+    TimeSlot possibleFittingSlot = new TimeSlotImpl(hasNext ? nextAppointment.end() : startOfDay(),
+        startOfBefore == null ? endOfDay() : startOfBefore);
+
+    if (possibleFittingSlot.fits(toFind)) {
+      goodSlots.add(possibleFittingSlot);
+    }
+
+    if (!hasNext) {
+      return goodSlots;
+    }
+
+    return traverseGapsFitting(toFind, goodSlots, nextAppointment.start(), iterator);
+
+  }
+
   @Override
   public List<TimeSlot> findGapsFitting(Duration duration) {
-    // TODO Auto-generated method stub
-    throw new UnsupportedOperationException("Unimplemented method 'findGapsFitting'");
+    return new CustomListToJavaBinding<>(
+        traverseGapsFitting(duration, new CustomLinkedListImpl<>(), null, timeline.iterator()));
   }
 
   @Override