Coding for Interview: Level Order Tree Print

bfs.py

def bfs(root):
    nodes = [(0,root)]
    prev_level = 0
    while nodes:
        level, node = nodes.pop(0)
        if level > prev_level:
            print
        print node.value,
        prev_level = level
        for c in node.children:
            nodes.append((level+1, c))

class Node:
    def __init__(self, value, children=None):
        self.value = value
        self.children = children if children else []

if __name__ == "__main__":
    root = Node(3, [Node(9), Node(20, [Node(15), Node(17)])])
    bfs(root)