Sword finger offer 32 - I. print binary tree from top to bottom

The finger of the sword Offer 32 - I. Print binary from top to bottom

• Binary tree   Top to bottom   Print （ Print by layer ）, Also known as binary tree   Breadth first search （BFS）.
• BFS Usually with   queue   The first in first out feature of .

import collections


class TreeNode:
    def __init__(self, x):
        self.val = x
        self.left = None
        self.right = None
class Solution:
    def levelOrder(self,root):
        res,qu=[],collections.deque()
        if bool(root)==0:
            return []
        qu.append(root)
        while qu:
            tmp=qu.popleft()
            res.append(tmp.val)
            if tmp.left:
               qu.append(tmp.left)
            if tmp.right:
               qu.append(tmp.right)
        return res