Is N-ary Tree Level Order Traversal easy or hard?

This problem is usually rated Medium because the core BFS idea is simple but requires handling a variable number of children for each node. Candidates comfortable with binary tree level order traversal can adapt the same pattern to N-ary trees quickly.

N-ary Tree Level Order Traversal Python/Java solution

Python and Java solutions typically implement BFS with a queue (collections.deque in Python or LinkedList/ArrayDeque in Java). The algorithm processes nodes level by level and collects values into nested lists representing each depth. Both implementations run in O(n) time and O(w) space.

How to solve N-ary Tree Level Order Traversal in O(n)?

Use Breadth-First Search with a queue. Start by pushing the root node into the queue, then repeatedly process nodes level by level using the queue size to separate levels. For each node, append its value to the current level list and enqueue all its children. Since each node is processed once, the total runtime remains O(n).

What is the best approach for N-ary Tree Level Order Traversal?

The best approach is Breadth-First Search (BFS) using a queue. BFS naturally processes nodes level by level, which matches the requirement of level order traversal. Each level is processed by iterating the current queue size and pushing all children of those nodes. This approach runs in O(n) time and uses O(w) space where w is the maximum width of the tree.

Is N-ary Tree Level Order Traversal asked at Google/Amazon/Meta?

Level order traversal problems are common in interviews at companies like Amazon, Google, and Meta because they test tree traversal fundamentals and BFS understanding. Variants appear in many interview question banks, especially when working with N-ary trees or graph-like structures.

What data structure is used in N-ary Tree Level Order Traversal?

A queue is the primary data structure used for the iterative solution. The queue stores nodes of the current level while their children are added for the next level. This structure enables first-in-first-out processing required for breadth-first traversal.

What is the time complexity of N-ary Tree Level Order Traversal?

The time complexity is O(n) because every node in the N-ary tree is visited exactly once. Each node is dequeued once and its children are added to the queue once. The total operations scale linearly with the number of nodes.

Description Solution Video 6:15

429. N-ary Tree Level Order Traversal

Medium71.6% acceptance3 companies

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: