Fixed a bug in the getHeadValue of the Heap structures

Author: phishman3579

src/com/jwetherell/algorithms/data_structures/BinaryHeap.java

@@ -372,7 +372,7 @@ public String toString() {
         protected static class HeapPrinter {
 
             public static <T extends Comparable<T>> String getString(BinaryHeapArray<T> tree) {
-                if (tree.array.length == 0)
+                if (tree.size == 0 || tree.array.length == 0)
                     return "Tree has no nodes.";
 
                 T root = tree.array[0];