Max Width of Binary Tree

7    while queue:
●        level_size = len(queue)
9        _, first = queue[0]; _, last = queue[-1]
10        ans = max(ans, last - first + 1)
11        for _ in range(level_size):
12            node, idx = queue.popleft()
13            idx -= first
14            if node.left:
15                queue.append((node.left, 2 * idx + 1))
16            if node.right:
17                queue.append((node.right, 2 * idx + 2))
18    return ans