429-n-ary-tree-level-order-traversal.py

"""
Problem Link: https://leetcode.com/problems/n-ary-tree-level-order-traversal/

Given an n-ary tree, return the level order traversal of its nodes' values.
Nary-Tree input serialization is represented in their level order traversal, 
each group of children is separated by the null value. 

Example 1:
Input: root = [1,null,3,2,4,null,5,6]
Output: [[1],[3,2,4],[5,6]]

Example 2:
Input: root = [1,null,2,3,4,5,null,null,6,7,null,8,null,9,10,null,null,11,null,12,null,13,null,null,14]
Output: [[1],[2,3,4,5],[6,7,8,9,10],[11,12,13],[14]]
 
Constraints:
The height of the n-ary tree is less than or equal to 1000
The total number of nodes is between [0, 10^4]
"""
"""
# 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]]:
        res = []
        if not root:
          return res
        
        queue = [root]
        while queue:
          next_level = []
          cur_level_val = []
          
          for cur_node in queue:
            cur_level_val.append(cur_node.val)
            if cur_node.children:
              next_level.extend(cur_node.children)
              
          queue = next_level
          res.append(cur_level_val)
        return res