leetcode.110 balanced binary tree

 * 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 (TreeNode* root) {
        if(root == nullptr)
            return true;
        if(root->left == nullptr && root->right == nullptr)
            return true;
        if(abs(depth(root->left) - depth(root->right)) > 1)
            return false;
        return isBalanced(root->left) && isBalanced(root->right);
        
    }
private:
    int depth(TreeNode *root)
    {
        if(root == nullptr)
            return 0;
        return max(depth(root->left), depth(root->right)) + 1;
    }
};