【leetcode】剑指 Offer 32 - II. 从上到下打印二叉树 II（python）

思路： 一开始没想好怎么控制打印每层多少个，后来发现可以依据队列长度进行控制。

# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None
import collections
class Solution(object):
    def levelOrder(self, root):
        """
        :type root: TreeNode
        :rtype: List[List[int]]
        """
        if root == None:  # 空树
            return []
        result = [] 
        que = collections.deque() 
        que.append(root)
        while que:
            tmp_lst = []
            for i in range(len(que)):
                poped = que.popleft()
                tmp_lst.append(poped.val)
                if poped.left:
                    que.append(poped.left)
                if poped.right:
                    que.append(poped.right)
            result.append(tmp_lst)
        return result