059 按之字形顺序打印二叉树

题目描述
请实现一个函数按照之字形打印二叉树，即第一行按照从左到右的顺序打印，第二层按照从右至左的顺序打印，第三行按照从左到右的顺序打印，其他行以此类推。
示例1
输入
{8,6,10,5,7,9,11}
返回值
[[8],[10,6],[5,7,9,11]]

# -*- coding:utf-8 -*-
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None
class Solution:
    def Print(self, pRoot):
        # write code here
        if not pRoot:
            return []
        flag=0
        list=[pRoot]
        result=[]  
        while list:
            mid=[]
            nextceng=[]           
            for i in list:
                mid.append(i.val)
                if i.left:
                    nextceng.append(i.left)
                if i.right:
                    nextceng.append(i.right)
                list=nextceng              
            if flag%2==1:
                mid.reverse()
            result.append(mid)
            flag+=1
        return  result