#Leetcode# 110. Balanced Binary Tree

https://leetcode.com/problems/balanced-binary-tree/

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.

Example 1:

Given the following tree [3,9,20,null,null,15,7]:

    3
   / 
  9  20
    /  
   15   7

Return true.

Example 2:

Given the following tree [1,2,2,3,3,null,null,4,4]:

       1
      / 
     2   2
    / 
   3   3
  / 
 4   4

Return false.

代码：

/**
 * 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 isBalanced(TreeNode* root) {
        if(!root) return true;
        int l = maxDepth(root -> left);
        int r = maxDepth(root -> right);
        return abs(l - r) <= 1 && isBalanced(root -> left) && isBalanced(root -> right);
    }
    int maxDepth(TreeNode* root) {
        if(!root) return 0;
        int h1 = 1, h2 = 1;
        if(root -> left != NULL)
            h1 = maxDepth(root -> left) + 1;
        if(root -> right != NULL)
            h2 = maxDepth(root -> right) + 1;
        return max(h1, h2);
    }
};

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