【Leetcode】107—Binary Tree Level Order Traversal II

一、题目描述

给定一个二叉树，返回其节点值自底向上的层次遍历。 （即按从叶子节点所在层到根节点所在的层，逐层从左向右遍历）

二、代码实现

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# 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 levelOrderBottom(self, root):
        """
        :type root: TreeNode
        :rtype: List[List[int]]
        """
        if root == None: return []
        queue = [root]
        res = []
        while len(queue):
            layer = []
            for i in range(len(queue)):
                cur = queue.pop(0)
                layer.append(cur.val)
                if cur.left: queue.append(cur.left)
                if cur.right: queue.append(cur.right)
            res.append(layer)
        return res[::-1]