Prep RoomSign inStart free
Code RoomUnchecked map lookup crashes
MediumPrep Room Coding #4214

Unchecked map lookup crashes

Vibe & agenticAlgorithms & data structuresMid–Senior~15 min

An AI wrote this Kotlin code in an Android mobile game to look up a level's config and start it. It works for the campaign levels the dev tested, but crashes with a NullPointerException when players reach community-made or seasonal levels. What's the bug and how would you catch it?

Implement
resolve_level_track(level_ids: list[str], level_themes: list[str], soundtrack_themes: list[str], requested_id: str) → str
Examples
in[["c1","c2","s1"],["forest","cave","winter"],["forest","cave"],"c2"]out"track:cave"
in[["c1","c2","s1"],["forest","cave","winter"],["forest","cave"],"s1"]out"track:default"
in[["c1","c2","s1"],["forest","cave","winter"],["forest","cave"],"ugc-9134"]out"missing_level"
What a strong answer looks like

Treat the AI’s output as a draft to verify, not an answer to trust. Name the specific flaw and the input that triggers it, say how you’d catch it (tests, edge cases, reading critically), and how you’d re-prompt or decompose to get it right.

0:00 of about 15 min

Vibe & agentic: describe the solution in plain language (or narrate it) and the coach grades your approach.

Which questions mattered is sealed until you submit. Telling you now would just be handing over the edge cases.