lab10

lab10/ArrayHeap.java

@@ -104,7 +104,7 @@ private void swim(int index) {
         // Throws an exception if index is invalid. DON'T CHANGE THIS LINE.
         validateSinkSwimArg(index);
         // 0. check if the given node's parent is index 0 or null;
-        if (parentIndex(index) == 0) return;
+        if (index == 1) return;
         // 1. check if the given node is smaller than its parent
         // 2. if not, return
         // 3. if yes, get the parent index,
@@ -173,11 +173,12 @@ public T peek() {
      */
     @Override
     public T removeMin() {
+        if (size == 0) return null;
         T returnNode = peek();
         swap(size, 1);
         contents[size] = null;
         size -= 1;
-        sink(1);
+        if (size > 0) sink(1);
         return returnNode;
     }
 
@@ -208,13 +209,15 @@ public void changePriority(T item, double priority) {
                 break;
             }
         }
+
         // 2. update its priority
         Node updatedNode = new Node(item, priority);
         contents[targetIndex] = updatedNode;
         // 3. compare the updated node with its parent and minChild
         //      to determine if it should swim (p) or sink(c)
         int p = parentIndex(targetIndex);
         int c = min(leftIndex(targetIndex), rightIndex(targetIndex));
+        if (p == 0 || c > size) return;
         if (min(targetIndex, p) == targetIndex) swim(p);
         else if (min(targetIndex, c) == c) sink(c);
         else return;