【剑指offer】按之字形顺序打印二叉树（python）

思路类似于“把二叉树打印成多行”，添加一个flag，表示从左到右还是从右到左，如果是从右到左就把tmp反转添加到result里。

# -*- 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
        queue = []
        result = []
        queue.append(pRoot)
        left_to_right = True
        while queue:
            num = len(queue)
            tmp = []
            for i in range(num):
                node = queue.pop(0)
                if node is None:
                    continue
                tmp.append(node.val)
                queue.append(node.left)
                queue.append(node.right)
            if tmp:
                if left_to_right:
                    result.append(tmp)
                else:
                    tmp.reverse()
                    result.append(tmp)
            left_to_right = not left_to_right
        return result