def topView(root):
    if not root:
        return
    
    hd_map = {}
    
    queue = deque([(root, 0)])
    
    while queue:
        node, hd = queue.popleft()
        if hd not in hd_map:
            hd_map[hd] = node.info
            
        if node.left:
            queue.append((node.left, hd - 1))
        if node.right:
            queue.append((node.right, hd + 1))
    for hd in sorted(hd_map.keys()):
        print(hd_map[hd], end=" ")