BalancedBinaryTree

Change-Id: If9f723c145b20b9a8ef6e66cf0e14d88c96ffaa5

Author: applewjg

BalancedBinaryTree.java

@@ -0,0 +1,36 @@
+/*
+ Author:     King, [email protected]
+ Date:       Oct 07, 2014
+ Problem:    Balanced Binary Tree
+ Difficulty: Easy
+ Source:     https://oj.leetcode.com/problems/balanced-binary-tree/
+ Notes:
+ Given a binary tree, determine if it is height-balanced.
+ For this problem, a height-balanced binary tree is defined as a binary tree in which 
+ the depth of the two subtrees of every node never differ by more than 1.
+
+ Solution: DFS.
+ */
+/**
+ * Definition for binary tree
+ * public class TreeNode {
+ *     int val;
+ *     TreeNode left;
+ *     TreeNode right;
+ *     TreeNode(int x) { val = x; }
+ * }
+ */
+public class Solution {
+    public boolean isBalanced(TreeNode root) {
+        if (root == null) return true;
+        return isBalancedRe(root) > -1;
+    }
+    public int isBalancedRe(TreeNode root) {
+        if (root == null) return 0;
+        int left = isBalancedRe(root.left);
+        int right = isBalancedRe(root.right);
+        if (left == -1 || right == -1) return -1;
+        if (Math.abs(left - right) > 1) return -1;
+        return Math.max(left, right) + 1;
+    }
+}