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.
Input: root = [3,9,20,null,null,15,7] Output: true
Input: root = [1,2,2,3,3,null,null,4,4] Output: false
Input: root =  Output: true
-104 <= Node.val <= 104