Python3解leetcode N-ary Tree Level Order Traversal

问题描述：

Given an n-ary tree, return the level order traversal of its nodes' values. (ie, from left to right, level by level).

For example, given a 3-ary tree:

We should return its level order traversal:

[
     [1],
     [3,2,4],
     [5,6]
]

Note:

1. The depth of the tree is at most 1000.
2. The total number of nodes is at most 5000.

思路：此题是在leetcode上见到的第一个BFS的题目，因而记录。同时注意该句代码应用方式 Node,level = queue.pop()

代码：

"""
# Definition for a Node.
class Node:
    def __init__(self, val, children):
        self.val = val
        self.children = children
"""
class Solution:
    def levelOrder(self, root: 'Node') -> List[List[int]]:
        if not root:
            return []
        
        result, queue = [],[(root,1)]
        while queue:
            Node,level = queue.pop()
            if level - len(result) >= 1:
                result.append([])
            result[level - 1].append(Node.val)
            
            for child in Node.children:
                queue.insert(0,(child,level+ 1))
        return result