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.*//** * 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) return true;        return depth(root)!=-1;    }    int depth(TreeNode* root)    {        if(!root) return 0;        int leftdepth=depth(root->left);        if(leftdepth==-1) return -1;        int rightdepth=depth(root->right);        if(rightdepth==-1) return -1;        if(abs(leftdepth-rightdepth)>1) return -1;        return max(leftdepth,rightdepth)+1;    }};