Cây nhị phân cân bằng

def is_balanced_opt(root):
    if isinstance(root, list):
        r = build_tree(root)
        return is_balanced_opt_helper(r)
    return is_balanced_opt_helper(root)

def is_balanced_opt_helper(root: TreeNode) -> bool:
    def check(node):
        if not node:
            return 0
        left = check(node.left)
        if left == -1: return -1
        right = check(node.right)
        if right == -1: return -1
        if abs(left - right) > 1: return -1
        return 1 + max(left, right)
    return check(root) != -1

def is_balanced_brute(root):
    if isinstance(root, list):
        r = build_tree(root)
        return is_balanced_brute_helper(r)
    return is_balanced_brute_helper(root)

def is_balanced_brute_helper(root: TreeNode) -> bool:
    if not root:
        return True
    def height(node):
        if not node: return 0
        return 1 + max(height(node.left), height(node.right))
    left_h = height(root.left)
    right_h = height(root.right)
    return abs(left_h - right_h) <= 1 and is_balanced_brute_helper(root.left) and is_balanced_brute_helper(root.right)