判断一个树是不是平衡树

/**
* 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:
    ///unordered_map<TreeNode *,int> m;
   
    int getDepth(TreeNode *node)
    {
        if(!node)
            return 0;
        return node->val;
    }
       
    bool isBalanced(TreeNode* root) {
        if(root==NULL){
            return true;
        }
       
        if(isBalanced(root->left)==false)
            return false;
        if(isBalanced(root->right)==false)
            return false;
           
        int dep_left = getDepth(root->left);
        int dep_right = getDepth(root->right);
       
        if(abs(dep_left-dep_right)>1)
            return false;
       
        root->val = 1 + (dep_left > dep_right ? dep_left : dep_right);
        return true;
    }

  
};