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

题意：

Given a binary tree, return the bottom-up level order traversal of its nodes' values. (ie, from left to right, level by level from leaf to root).

For example:

Given binary tree {3,9,20,#,#,15,7},

3   / \  9  20    /  \   15   7

 

return its bottom-up level order traversal as:

[  [15,7]  [9,20],  [3],]

 

confused what "{1,#,2,3}" means? 

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

The above binary tree is serialized as 

"{1,2,3,#,#,4,#,#,5}".

解题思路：由于编程语言为python，所以其实在Binary Tree Level Order Traversal这道题（http://www.cnblogs.com/zuoyuan/p/3722004.html）的基础上加一句res.reverse()就可以了。

代码：

# Definition for a  binary tree node# class TreeNode:#     def __init__(self, x):#         self.val = x#         self.left = None#         self.right = Noneclass 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([])            res[level].append(root.val)            self.preorder(root.left, level+1, res)            self.preorder(root.right, level+1, res)                def levelOrderBottom(self, root):        res=[]        self.preorder(root, 0, res)        res.reverse()        return res