top view python

# http://code2begin.blogspot.com
# Program to print the top view of the binary tree
# node class
class node:
    def __init__(self, element):
        self.data = element
        self.hd = -1
        self.left = None
        self.right = None


# function to print the top view of the binary tree
def top_view(root):
    if root is None:
        return

    # we keep track of the horizontal distance of the node from the root node
    # to print the bottom view
    # hd = horizontal distance from the root node
    # creating a Queue for storing node for level wise traversal
    # and a map for mapping horizontal distances with the node data
    Q = []
    Map = dict()

    Q.append(root)
    while len(Q) > 0:

        # pop the first node from the queue
        p = Q[0]
        del Q[0]

        hd = p.hd

        # if a horizontal distance is already mapped with a value then
        # we don't replace it with a new value
        if hd not in Map.keys():
            Map[hd] = p.data

        # increase the horizontal distance from the root node in negative direction
        # and push the node on queue
        if p.left is not None:
            p.left.hd = hd - 1
            Q.append(p.left)

        # increase the horizontal distance from the root node in positive direction
        # and push the node on queue
        if p.right is not None:
            p.right.hd = hd + 1
            Q.append(p.right)

    # print the generated map
    print("Top view of the binary tree is : ")
    print(list(Map.values()))



head = node(1)
head.left = node(2)
head.right = node(3)
head.left.left = node(4)
head.left.right = node(5)
head.right.right = node(6)
head.left.left.right = node(7)
head.right.right.left = node(8)
head.left.left.right.left = node(9)
head.left.left.right.left.left = node(10)
head.right.right.left.right = node(11)
head.hd = 0
top_view(head)