Implement a rate limiter and a pub/sub API

You have two coding/design (low-level design) tasks. ## 1) Rate limiter Design and implement a rate limiter with an API like: - `boolean allow(String clientId)` or `boolean allow(String key)` It should enforce a policy such as: - **N requests per time window** (e.g., 100 requests per minute) Discuss (and ideally implement) thread-safety and how you would adapt it for multiple application instances. ## 2) Pub/Sub Design and implement a simple Pub/Sub component (Java-like interfaces are fine), supporting: - `publish(topic, message)` - `subscribe(topic, subscriber)` - `unsubscribe(topic, subscriber)` Clarify delivery semantics (best-effort vs at-least-once), ordering per topic, and how you handle slow consumers.