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

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）

# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution(object):
    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):
        """
        :type root: TreeNode
        :rtype: List[List[int]]
        """
        res = []
        self.preorder(root, 0, res)
        res.reverse()
        print res
        return res