[leetcode 110] 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 left and right subtrees of every node differ in height by no more than 1.

 

Example 1:

Input: root = [3,9,20,null,null,15,7] Output: true

Example 2:

Input: root = [1,2,2,3,3,null,null,4,4] Output: false

Example 3:

Input: root = [] Output: true

 

Constraints:

• The number of nodes in the tree is in the range [0, 5000].
• -104 <= Node.val <= 104

문제 풀이:

모든 서브트리에 대해 balanced tree임을 확인해야 한다. 

 

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    
    int getHeight(TreeNode* cur){
        if(!cur) return 0;
        return max(getHeight(cur->left), getHeight(cur->right)) + 1;
    }
  
    bool isBalanced(TreeNode* root) {
        
        if(!root) return true;
       
        int left = getHeight(root->left);
        int right = getHeight(root->right);
        
        if( abs(left - right) > 1) return false;
        
        return isBalanced(root->left) && isBalanced(root->right);
        
    }
};