Code Room
CodingMedium
Question
Given a binary tree as a level-order array `arr` (null for missing), return its zigzag (boustrophedon) level-order traversal: the first level left to right, the second right to left, alternating thereafter. Return a list of lists of values, one per level. `0 <= node count <= 2000`.
Implement
zigzag_level_order(arr: list[int]) → list[list[int]]Examples
in
[[3,9,20,null,null,15,7]]out[[3],[20,9],[15,7]]What a strong answer looks like
State your approach and its time/space complexity out loud before you optimize. Handle the edge cases (empty input, duplicates, overflow), and say why you chose this over the brute force. Green tests are the floor, not the grade.
Learn the concepts
Vibe coding: describe the solution in plain language (or narrate it) and the coach grades your approach. Generating runnable code from your description is coming next.
Run or narrate your approach, then ask the coach.