429. N-ary Tree Level Order Traversal

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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 (See examples).

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]
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Intuition

Typical level order BFS using queue

Add root to tree
While Q is not Empty
pop elements at current level
Add child elements to end of Q

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Time - O(n)
Space - O(n)
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