# Implement and Test a Sliding-Window Rate Limiter Design an in-memory limiter with `allow(key, timestamp)` for a configurable maximum number of requests in the preceding window. ### Constraints & Assumptions - Timestamps for one key are nondecreasing. - Rejected requests do not consume capacity. ### Clarifying Questions to Ask - Is the interval left-open or left-closed? - Is the limit per process or global? ### What a Strong Answer Covers - Per-key eviction, boundary semantics, concurrency, and cleanup. - Focused tests for bursts and exact cutoffs. ### Follow-up Questions - How would you distribute the limiter? - What changes if rejected requests count?