Leetcode 110 Balanced Binary Tree 二叉树

判断一棵树是否是平衡树，即左右子树的深度相差不超过1.

我们可以回顾下depth函数其实是Leetcode 104 Maximum Depth of Binary Tree 二叉树

 /**
  * 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:
     int depth(TreeNode* root){
         if(!root) return ;
         else{
             return max(depth(root->left), depth(root->right)) + ;
         }
     }
     bool isBalanced(TreeNode* root) {
         if(!root) return true;
         else if(abs(depth(root->left) - depth(root->right))> ){
             return false;
         }
         else return isBalanced(root->left) && isBalanced(root->right);
     }
 };