Started with a deque and just popped off anything older than 5 minutes on each call.
Start by clarifying requirements and constraints, then implement a simple solution using a queue and a hash map for O(1) operations. For high traffic, discuss optimizations like bucketed time windows, sharding, and approximate counting with probabilistic data structures.
Pro tip: Mention that you would use a ring buffer of time buckets to avoid per-hit locking and enable lock-free reads, and discuss how to handle out-of-order timestamps and clock skew.
Ask about expected traffic volume, latency requirements, and whether exact counts are needed. Confirm the definition of 'last 5 minutes' (sliding window vs. fixed buckets).
Use a queue to store timestamps of hits and a counter for the current window. On each hit, enqueue timestamp and increment counter; on query, dequeue timestamps older than 5 minutes and decrement counter.
Identify that the simple solution has O(1) amortized time but may suffer from lock contention and memory growth under high traffic. Discuss the need for concurrency control.
Propose bucketed time windows (e.g., 1-second buckets) with a ring buffer to reduce lock contention and enable lock-free reads. Consider sharding by key (e.g., page URL) and using approximate counting (e.g., Count-Min Sketch) if exact counts are not required.
Compare exact vs. approximate counting, memory vs. accuracy, and latency vs. consistency. Mention distributed systems considerations like using Redis or a time-series database for scalability.
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