leetcode Balanced Binary Tree

 1 /**
 2  * Definition for binary tree
 3  * public class TreeNode {
 4  *     int val;
 5  *     TreeNode left;
 6  *     TreeNode right;
 7  *     TreeNode(int x) { val = x; }
 8  * }
 9  */
10 public class Solution {
11     
12         private int heightOfTree(TreeNode root) {
13         int height;
14         if (root == null) {
15             return -1;
16         }
17         
18         int hleft=heightOfTree(root.left);
19         int rlegt=heightOfTree(root.right);
20         height=1+Math.max(hleft, rlegt);
21         return height;
22     }
23     
24     public boolean isBalanced(TreeNode root) {
25         if (root == null) {
26             return true;
27         }
28         int height=heightOfTree(root.left)-heightOfTree(root.right);
29         if (height>1 || height<-1) {
30             return false;
31         }
32         if (!isBalanced(root.left)) {
33             return false;
34         }
35         if (!isBalanced(root.right)) {
36             return false;
37         }
38         return true;
39         
40     }
41 }