MaxHeap remove element and Sift Down.

liusishan · Feb 25, 2019 · af9920d · af9920d
1 parent 739313a
commit af9920d
Showing 1 changed file with 39 additions and 0 deletions.
diff --git a/08-Heap-and-Priority-Queue/01-Heap-Basics/01-Heap-Basics/src/MaxHeap.java b/08-Heap-and-Priority-Queue/01-Heap-Basics/01-Heap-Basics/src/MaxHeap.java
@@ -57,4 +57,43 @@ private void siftUp(int k) {
  }
  }
 
+ // 看堆中最大元素
+ public E findMax() {
+ if (data.getSize() == 0)
+ throw new IllegalArgumentException("Can not findMax when head is Empty.");
+ return data.get(0);
+ }
+
+ // 取出堆中最大元素
+ public E extractMax() {
+
+ E ret = findMax();
+
+ data.swap(0, data.getSize() - 1);
+ data.removeLast();
+ siftDown(0);
+
+ return ret;
+ }
+
+ // 下沉
+ private void siftDown(int k) {
+
+ while (leftChild(k) < data.getSize()) {
+
+ int j = leftChild(k);
+ if (j + 1 < data.getSize() &&
+ data.get(j + 1).compareTo(data.get(j)) > 0) { // 右孩子
+ j = rightChild(k);
+ }
+ // data[j] 是leftChild 和rightChild中的最大值
+
+ if (data.get(k).compareTo(data.get(j)) >= 0)
+ break;
+
+ data.swap(k, j);
+ k = j;
+ }
+ }
+
 }