I spent the first few minutes just generating timestamps and almost forgot to ask anything.
Start by clarifying requirements and constraints, then outline a two-part solution: an algorithm to generate the notification schedule for a single user and a scalable architecture to handle millions of users. Discuss trade-offs between batch processing and real-time generation, and how to ensure chronological ordering and fault tolerance.
Pro tip: Emphasize idempotency and exactly-once delivery semantics, as duplicate or missed notifications can erode user trust and are critical in a payments company like Stripe.
Ask about the expected scale, time window size, cadence types, time zones, and whether notifications can be batched or must be sent individually. Confirm if the schedule is precomputed or generated on-demand.
For each user, compute the next notification times based on their start time and cadence within the given window. Use efficient date arithmetic and handle edge cases like custom intervals and time zones.
Collect all notification events from all users and sort them chronologically. Consider using a priority queue or merge sort if processing in batches to avoid loading everything into memory.
Propose a distributed architecture: shard users by user ID or time zone, process shards in parallel, and use a message queue to decouple schedule generation from sending. Discuss storage and indexing for efficient retrieval.
Discuss idempotency, retries, dead-letter queues, and monitoring. Compare batch vs. real-time processing, and explain how to handle failures and ensure exactly-once delivery.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.