Question ：

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.

Anwser 1 ：

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    int maxHeight(TreeNode *root) {  
        if (root == NULL) return 0;  
          
        int left = maxHeight(root->left) + 1;  
        int right = maxHeight(root->right) + 1;  
        return left > right ? left : right;  
    } 
    
    bool isBalanced(TreeNode *root) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        if (root == NULL) return true;
        
        while(root != NULL)
        {
            int left = maxHeight(root->left);
            int right = maxHeight(root->right);
            if (abs(left - right) >= 2) {
                return false;
            }
            
            return isBalanced(root->left) && isBalanced(root->right);
        }
    }
};