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 binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
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;
		if(std::abs(dfs(root->left) - dfs(root->right)) > 1) return false;
		return isBalanced(root->left) && isBalanced(root->right);
    }
private:
	int dfs(TreeNode *root)
	{
		if(root == NULL) return 0;
		return std::max(dfs(root->left),dfs(root->right)) + 1;
	}
};

leetcode - Balanced Binary Tree