[leetcode]Binary Tree Zigzag Level Order Traversal @ Python

原题地址：http://oj.leetcode.com/problems/binary-tree-zigzag-level-order-traversal/

题意：

Given a binary tree, return the zigzag level
order traversal of its nodes‘ values. (ie, from left to right, then
right to left for the next level and alternate between).

For example:
Given binary tree {3,9,20,#,#,15,7},

    3

   /   9  20

    /     15   7

return its zigzag level order traversal as:

[

  [3],

  [20,9],

  [15,7]

]

confused
what "{1,#,2,3}" means? >
read more on how binary tree is serialized on OJ.

OJ‘s Binary Tree Serialization:

The serialization of a binary tree follows a level order traversal, where ‘#‘
signifies a path terminator where no node exists below.

Here‘s an example:

   1

  /  2   3

    /

   4

         5

解题思路：这道题和层序遍历那道题差不多，区别只是在于奇数层的节点要翻转过来存入数组。http://www.cnblogs.com/zuoyuan/p/3722004.html

代码：

# Definition for a  binary tree node

# class TreeNode:

#     def __init__(self, x):

#         self.val = x

#         self.left = None

#         self.right = None

class Solution:

    # @param root, a tree node

    # @return a list of lists of integers

    def preorder(self, root, level, res):

        if root:

            if len(res) < level+1: res.append([])

            if level % 2 == 0: res[level].append(root.val)

            else: res[level].insert(0, root.val)

            self.preorder(root.left, level+1, res)

            self.preorder(root.right, level+1, res)

    def zigzagLevelOrder(self, root):

        res=[]

        self.preorder(root, 0, res)

        return res

[leetcode]Binary Tree Zigzag Level Order Traversal @
Python,布布扣,bubuko.com

[leetcode]Binary Tree Zigzag Level Order Traversal @
Python