[LeetCode]题解（python）：107 Binary Tree Level Order Traversal II

Posted 2020-07-06 loadofleaf

题目来源

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https://leetcode.com/problems/binary-tree-level-order-traversal-ii/

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).

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题意分析

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Input: binary tree

Output: list

Conditions:输出每层的集合，注意是反向输出，即最后一层的先输出

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题目思路

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同I，将res反置即可

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AC代码（Python）

 1 # Definition for a binary tree node.
 2 # class TreeNode(object):
 3 #     def __init__(self, x):
 4 #         self.val = x
 5 #         self.left = None
 6 #         self.right = None
 7 
 8 class Solution(object):
 9     def preorder(self, root, level, res):
10         if root:
11             if len(res) < level + 1: res.append([])
12             res[level].append(root.val)
13             self.preorder(root.left, level + 1, res)
14             self.preorder(root.right, level + 1, res)
15     def levelOrderBottom(self, root):
16         """
17         :type root: TreeNode
18         :rtype: List[List[int]]
19         """
20         res = []
21         self.preorder(root, 0, res)
22         res.reverse()
23         print res
24         return res