LeetCode110. Balanced Binary Tree

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;
    }
};