Design In-Memory QPS Counter

Implement an in-memory traffic counter. You need to support two operations for each logical key, such as an endpoint, customer, or service name: - `record(key, timestamp)`: a request for `key` happened at `timestamp`. - `get_qps(key, now)`: return the average queries per second for `key` over the last 5 minutes, using the time window `[now - 299, now]`. Requirements: - All data must be stored in memory. - Timestamps are integer seconds. - Multiple requests may arrive with the same `key` and the same `timestamp`. - Start with a working solution for a 5-minute sliding window. Follow-up discussion: 1. How would you reduce memory usage? 2. How would you extend the design to support a 24-hour window? 3. How would you efficiently handle many requests that share the same timestamp? Assume calls arrive in non-decreasing timestamp order.