Given a binary tree, determine if it is height-balanced.
A height-balanced binary tree is a binary tree in which the depth of the two subtrees of every node never differs by more than one.
[0, 5000]-10^4 <= Node.val <= 10^4root = [3,9,20,null,null,15,7]trueroot = [1,2,2,3,3,null,null,4,4]falseroot = []true