'''
Description: 
Autor: Au3C2
Date: 2021-03-19 10:57:36
LastEditors: Au3C2
LastEditTime: 2021-03-19 10:57:56
'''
class Solution:
    def levelOrder(self, root: TreeNode) -> List[List[int]]:
        self.level_dict = dict()
        self.recursion(root,0)
        res = list(self.level_dict.values())
        return res

    def recursion(self,root,level):
        
        if not root:
            return
        if level in self.level_dict:
            self.level_dict[level].append(root.val)
        else:
            self.level_dict[level] = list([root.val])
        level += 1
        self.recursion(root.left,level)
        self.recursion(root.right,level)
        level -= 1

# 树，中等
# https://leetcode-cn.com/problems/binary-tree-level-order-traversal/