Python3解leetcode Same TreeBinary Tree Level Order Traversal II

问题描述：

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,null,null,15,7],

return its bottom-up level order traversal as:

[

  [15,7],

  [9,20],

  [3]

]

注意是每一层的所有数字放入同一个list内

思路：二叉树问题，考虑使用递归算法，计算出每一层的所有元素值

# Definition for a binary tree node.

# class TreeNode:

#     def __init__(self, x):

#         self.val = x

#         self.left = None

#         self.right = None

class Solution:

    def levelOrderBottom(self, root: TreeNode) -> List[List[int]]:

        if root == None: return []

        def order(rootx,level):

            if rootx == None:return

            if (level) == len(result):

                result.append([rootx.val])

            else:

                result[level].append(rootx.val)

            order(rootx.left,level+1)

            order(rootx.right,level+1)

        result = []

        order(root,0)

        return result[::-1]

巴特西

Python3解leetcode Same TreeBinary Tree Level Order Traversal II

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