Printing BFS (Binary Tree) in Level Order with Specific Formatting

Question

To begin with, this question is not a dup of this one, but builds on it.

Taking the tree in that question as an example,

    1 
   / \\
  2   3
 /            


        

Answer 1

This is breadth first search, so you can use a queue and recursively do this in a simple and compact way ...

# built-in data structure we can use as a queue
from collections import deque

def print_level_order(head, queue = deque()):
    if head is None:
        return
    print head.data
    [queue.append(node) for node in [head.left, head.right] if node]
    if queue:
        print_level_order(queue.popleft(), queue)