leetcode_110. Balanced Binary Tree

题目：

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.

直接的想法就是，比较做右子树的高度。而这个高度就等于此树左右子树最高的树的高度。所以代码如下：

/** * Definition for a binary tree node. * struct TreeNode { *     int val; *     TreeNode *left; *     TreeNode *right; *     TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */class Solution {public:    int depth(TreeNode* root){        if(root == NULL) return 0;        return 1+max(depth(root->left),depth(root->right));    }    bool isBalanced(TreeNode* root) {        if(root == NULL) return true;        return abs(depth(root->left) - depth(root->right))<=1 && isBalanced(root->left) && isBalanced(root->right);    }};