来源

https://leetcode-cn.com/problems/n-ary-tree-level-order-traversal/

题目描述

给定一个 N 叉树，返回其节点值的层序遍历。 (即从左到右，逐层遍历)。

例如，给定一个 3叉树 :

 
返回其层序遍历:

[
[1],
[3,2,4],
[5,6]]
 

说明:

树的深度不会超过 1000。
树的节点总数不会超过 5000。

代码实现

"""
# Definition for a Node.
class Node:
    def __init__(self, val=None, children=None):
        self.val = val
        self.children = children
"""
class Solution:
    def levelOrder(self, root: 'Node') -> List[List[int]]:
        if root is None:
            return []        

        result = []
        previous_layer = [root]

        while previous_layer:
            current_layer = []
            result.append([])
            for node in previous_layer:
                result[-1].append(node.val)
                current_layer.extend(node.children)
            previous_layer = current_layer
        return result