def topView(root):
    from collections import defaultdict
    queue=[(root,0)]
    hashtable=defaultdict(lambda:[]) 
    for node,level in queue: #level=x-coordinator
        if node!=None:
            hashtable[level].append(node.data) #hashtable, collect node data with the same level#
            queue.extend([(node.left,level-1),(node.right,level+1)]) #add node in sublevel to queue
    if hashtable !=None:
        for level in xrange(min(hashtable.keys()),max(hashtable.keys())+1):
            print hashtable[level][0], #TOPVIEW
    else:
        return None

def topView(root):
    #start with left most leaf
    if root.left:
        printleftside(root.left) #print left side top view, from bottom to top (left to right)
    print root.data, #print root
    if root.right:
        printrightside(root.right) #print right side top view, from top to bottom (left to right)

def printleftside(node):
    if node:
        printleftside(node.left)
    else:
        return
    print node.data,

def printrightside(node):
    if node:
        print node.data,
        printrightside(node.right)
    else:
        return