Design a time-based key-value store: set with a timestamp, get the value as of a time.

A time-based key-value store records versioned writes and answers 'what was the value at time t' via binary search over per-key timestamps. The signal is the append-only design and the floor (largest timestamp <= t) lookup. Here is the answer.

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