Build an in-memory key-value database, then extend it across stages: TTL, transactions, snapshots.
The classic multi-round build screen: a plain key-value store that gains new requirements at each stage (TTL, transactions, scans). The signal is not stage 1, it is whether your code takes on stage 4 without a rewrite. Here is how to design for it.
Updated Sep 2026 · Grounded in real GenAI, LLM, and AI/ML engineering interview loops and written to a senior-engineer editorial bar.
The classic multi-round build screen: a plain key-value store that gains new requirements at each stage (TTL, transactions, scans). The signal is not stage 1, it is whether your code takes on stage 4 without a rewrite. Here is how to design for it.
Lead with where the obvious approach breaks, because that is the judgment they are screening for — most candidates jump straight to the happy path and lose the room.
Then walk the failure back through the pipeline in order, naming the one metric the customer's exec sponsor actually cares about before you propose the fix.
