Problem Description

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.

Examples

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].
• $-10^4$ <= Node.val <= $10^4$

解析

給一個 二元樹的根結點 root 要判斷，該樹是不是 Balanced

定義一個 tree 是 balance tree 代表對 tree 所有結點的左右子結點高度差距不超過 1