leetcode 110. Balanced Binary Trees

Given a binary tree, determine whether it is a highly balanced binary tree.

In this problem, a height-balanced binary tree is defined as:

The absolute value of the height difference between the left and right subtrees of each node  of a binary tree does not exceed 1.

Example 1:

Given a binary tree [3,9,20,null,null,15,7]

    3
   / \
  9  20
    /  \
   15   7

return  true .

Example 2:

Given a binary tree [1,2,2,3,3,null,null,4,4]

       1
      / \
     2   2
    / \
   3   3
  / \
 4   4

return  false .

 

 1 /**
 2  * Definition for a binary tree node.
 3  * struct TreeNode {
 4  *     int val;
 5  *     TreeNode *left;
 6  *     TreeNode *right;
 7  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 8  * };
 9  */
10 class Solution {
11 public:
12     int getHeight(TreeNode* root){
13         if(root == NULL) return 0;
14         int l = getHeight(root->left);
15         int r = getHeight(root->right);
16         return l > r ? l+1 : r+1;
17     }
18     bool isBalanced(TreeNode* root) {
19         if(root == NULL) return true;
20         if(getHeight(root->left) - getHeight(root->right) > 1) return false;
21         else if(getHeight(root->right) - getHeight(root->left) > 1) return false;
22         else return isBalanced(root->left) && isBalanced(root->right);
23     }
24 };