一、题目

Given a binary tree, determine if it is
height-balanced
.

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

二、题解

/*** 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* root){if(root == nullptr) return 0;int leftHeight = getHeight(root->left);if(leftHeight == -1) return -1;int rightHeight = getHeight(root->right);if(rightHeight == -1) return -1;if(abs(leftHeight - rightHeight) > 1) return -1;else return 1 + max(leftHeight,rightHeight);}bool isBalanced(TreeNode* root) {return getHeight(root) != -1;}
};