[leetcode] Balanced Binary Tree

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.

给一棵二叉树，判断其是否为平衡二叉树。

使用递归，如果一棵树是平衡二叉树，那么他的左子树和右子树也应该是平衡二叉树，而且两子树的高度差不超过1。depth为该节点的深度初始化为0。

代码如下：

 1 /** 

 2  * Definition for binary tree 

 3  * struct TreeNode { 

 4  *     int val; 

 5  *     TreeNode *left; 

 6  *     TreeNode *right; 

 7  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {} 

 8  * }; 

 9  */ 

10 class Solution {  

11     public:  

12         bool isBalanced(TreeNode *root) {  

13             // Note: The Solution object is instantiated only once and is reused by each test case.  

14             int depth = 0;  

15             return isbalance(root, depth);  

16         }  

17         bool isbalance(TreeNode *root, int &depth)  

18         {  

19             if(root == NULL)  

20             {  

21                 depth = 0;  

22                 return true;  

23             }  

24             int ld,rd;  

25             if( isbalance(root->left,ld) && isbalance(root->right,rd))  

26             {  

27                 if( abs(ld - rd) > 1)  

28                 {  

29                     return false;  

30                 }  

31                 depth = ld > rd ? ld + 1 : rd + 1;  

32                 return true;  

33             }

34             else return false;

35         }  

36 };