heapify

src/main/java/git/snippet/heap/LintCode_0130_Heapify.java

@@ -6,33 +6,23 @@ package git.snippet.heap;
 // https://www.lintcode.com/problem/130/
 public class LintCode_0130_Heapify {
     public void heapify(int[] a) {
-        if (null == a || a.length <= 1) {
-            return;
-        }
-        for (int i = a.length - 1; i >= 0; i--) {
-            heapify(a, i, a.length);
-        }
-    }
-
-    public void heapify(int[] arr, int i, int len) {
-        int leftChildIndex = 2 * i + 1;
-        while (leftChildIndex < len) {
-            int min =
-                    leftChildIndex + 1 < len && arr[leftChildIndex + 1] < arr[leftChildIndex]
-                            ? leftChildIndex + 1
-                            : leftChildIndex;
-            min = arr[min] > arr[i] ? i : min;
-            if (min == i) {
-                break;
+        for (int index = a.length - 1; index >= 0; index--) {
+            int i = index;
+            int leftChildIndex = 2 * i + 1;
+            while (leftChildIndex < a.length) {
+                int minIndex = leftChildIndex + 1 < a.length && a[leftChildIndex] > a[leftChildIndex + 1] ? leftChildIndex + 1 : leftChildIndex;
+                minIndex = a[i] < a[minIndex] ? i : minIndex;
+                if (minIndex == i) {
+                    break;
+                }
+                swap(a, i, minIndex);
+                i = minIndex;
+                leftChildIndex = 2 * i + 1;
             }
-            swap(arr, min, i);
-            i = min;
-            leftChildIndex = 2 * min + 1;
         }
     }
-
     public void swap(int[] arr, int i, int j) {
-        if (i != j) {
+        if (i != j && arr != null && arr.length > 1) {
             arr[i] = arr[i] ^ arr[j];
             arr[j] = arr[i] ^ arr[j];
             arr[i] = arr[i] ^ arr[j];

src/main/java/git/snippet/heap/MaxHeap.java

@@ -22,12 +22,10 @@ package git.snippet.heap;
 // heapify和heapInsert都是logN级别的复杂度，因为N个节点的二叉树高度是logN
 public class MaxHeap {
     private final int[] heap;
-    // private final int limit; limit == heap.length
     private int heapSize;
 
     public MaxHeap(int limit) {
         heap = new int[limit];
-        // this.limit = limit;
         heapSize = 0;
     }