I went straight for a per-IP deque of timestamps, which felt right.
Start by clarifying requirements and constraints (e.g., window size, threshold, memory limits, distributed vs. single-node). Then propose a sliding window algorithm using a deque or circular buffer per IP, and discuss cleanup strategies like periodic pruning or lazy deletion. Finally, analyze time/space complexity and trade-offs, and consider extensions for scale.
Pro tip: Mention that you would use a hash map from IP to a deque of timestamps, and for cleanup, either periodically remove stale IPs or use a time-bucketed approach to avoid O(n) scans. Also, discuss how to handle out-of-order timestamps and the importance of monotonic clocks.
Ask about window size, threshold, expected number of IPs, memory limits, and whether the system is distributed. This shows you think before coding.
Propose a hash map from IP to a deque (or circular buffer) of timestamps within the window. Explain how record and isBot operations work.
For record, append timestamp and evict old ones. For isBot, count timestamps in window and compare to threshold. Discuss lazy vs. eager eviction.
Describe periodic cleanup of stale IPs (e.g., using a background thread or time-bucketed map) to prevent memory leaks. Discuss trade-offs between cleanup frequency and overhead.
State time complexity (O(1) amortized for record, O(k) for isBot where k is window size) and space complexity. Discuss alternatives like fixed windows or token buckets.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.