https://leetcode.com/problems/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==NULL){
            return true;
        }
        int depth=0;
        return isBalancedCore(root,depth);
    }
    bool isBalancedCore(TreeNode* root,int &depth){
        if(root==NULL){
            depth=0;
            return true;
        }
        int left,right;
        if(isBalancedCore(root->left,left)&& isBalancedCore(root->right,right)){
            depth=max(left,right)+1;
            int diff=left-right;
            if(diff>=-1 && diff<=1){
                return true;
            }
        }
        return false;
    }
};