110. 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.

判断一棵二叉树是否为平衡二叉树

C++（9ms）：

/**
 * 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:
    bool isBalanced(TreeNode* root) {
        if (root == NULL)
            return true ;
        return Depth(root) != -1 ;
    }
    
    int Depth(TreeNode* root) {
        if (root == NULL)
            return 0 ;
        int left = Depth(root->left) ;
        if (left == -1)
            return -1 ;
        int right = Depth(root->right) ;
        if (right == -1)
            return -1 ;
        if (abs(left - right) > 1)
            return -1 ;
        return max(left,right) + 1 ;
    }
};