429. N-ary Tree Level Order Traversal §

Date: 2026-01-31 Difficulty: Medium Topics: BFS, Tree, Level Order Traversal Link: https://leetcode.com/problems/n-ary-tree-level-order-traversal/

Final Solution §

class Solution:
    def levelOrder(self, root: 'Node') -> List[List[int]]:
        result = []
        if not root:
            return result
        queue = deque()
        queue.append(root)
        while queue:
            size = len(queue)
            curr_level = []
            for i in range(size):
                node = queue.popleft()
                curr_level.append(node.val)
                for child in node.children:
                    queue.append(child)
            result.append(curr_level)
        return result

Initial Issues §

• None - solved cleanly on first attempt

Key Learnings §

• N-ary vs Binary tree traversal: Only difference is how you add children
  • Binary: if node.left: queue.append(node.left) + same for right
  • N-ary: for child in node.children: queue.append(child)
• Same BFS level-order pattern applies regardless of tree structure

Nuances to Remember §

• node.children is a list (possibly empty), so iterating over it handles the “no children” case naturally
• No need to check if node.children before the loop - empty list just means zero iterations

Pattern Summary §

Fourth BFS problem in session - same core structure, different collection per level:

Problem	What you collect/do per level
116 - Next Pointers	Connect nodes via .next
1091 - Shortest Path	Count steps (distance)
429 - N-ary Traversal	Node values into lists