# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def isBalanced(self, root: Optional[TreeNode]) -> bool:
        return self.isBalanced_and_get_height(root)[0]


    def isBalanced_and_get_height(self, root):        
        # end of recursion
        if not root:
            return True, 0

        # split
        left_is_balanced, left_height = self.isBalanced_and_get_height(root.left) 
        right_is_balanced, right_height = self.isBalanced_and_get_height(root.right)

        # define
        if not (left_is_balanced and right_is_balanced):
            return False, -1

        if abs(left_height - right_height) > 1:
            return False, -1

        return True, max(left_height, right_height)+1