Top View of Binary Tree

6    first = {}
7    while queue:
●        node, hd = queue.popleft()
9        if hd not in first:
10            first[hd] = node.data
11        if node.left:
12            queue.append((node.left, hd - 1))
13        if node.right:
14            queue.append((node.right, hd + 1))
15    return [first[key] for key in sorted(first)]