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mediumOpenAIGleanScale

Build a versioned key-value store: put/get, plus get(key, timestamp) for historical reads

A multi-part favorite at OpenAI-style screens: simple store, then time travel, then deletes that don't actually delete. The append-only insight plus one bisect call solves the whole thing, if you set up the invariant correctly.

Updated Aug 2026 · Grounded in real Forward Deployed Engineer interview loops and written to a senior-engineer editorial bar.

A multi-part favorite at OpenAI-style screens: simple store, then time travel, then deletes that don't actually delete. The append-only insight plus one bisect call solves the whole thing, if you set up the invariant correctly.

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