is_tree_balanced.py

# Write a program that takes as input the root of a binary tree and checks whether the tree is height-balanced

import collections

def is_balanced_binary_tree(tree: BinaryTreeNode) -> bool:
    BalancedStatusWithHeight = collections.namedtuple(
        'BalancedStatusWithHeight', ('balanced', 'height')
    )


    def check_balanced(tree):
        if not tree:
            return BalancedStatusWithHeight(True, -1) # the base case

        left_result = check_balanced(tree.left)
        if not left_result.balanced:
            return BalancedStatusWithHeight(False, 0)
        
        right_result = check_balanced(tree.right)
        if not right_result.balanced:
            return BalancedStatusWithHeight(False, 0)

        is_balanced = abs(left_result.height - right_result.height) <= 1
        height = max(left_result.height, right_result.height) + 1
        return BalancedStatusWithHeight(is_balanced, height)


    return check_balanced(tree).balanced