Bottom View of Binary Tree

6    queue = deque([(root, 0)])
●    while queue:
8        node, hd = queue.popleft()
9        hd_to_val[hd] = node.data
10        if node.left: queue.append((node.left, hd - 1))
11        if node.right: queue.append((node.right, hd + 1))
12    return [hd_to_val[k] for k in sorted(hd_to_val)]