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  • [leetcode]Binary Tree Level Order Traversal II @ Python

    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? > 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
    
    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 = 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([])
                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
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  • 原文地址:https://www.cnblogs.com/zuoyuan/p/3722081.html
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