Stripe·Software Engineer·Technical Phone Screen·Intermediate

IntermediatePrefer not to say

May 2026Remote

Summary

Stripe coding interview with a scheduling problem that looks deceptively clean on the surface. One question, but it had enough edge cases to keep me busy for the whole session.

Questions Asked (1)

You have a list of user accounts, each with a subscription plan and a signup timestamp. You also have a schedule that maps email types (like welcome, upcoming expiry, expired) to time offsets relative to plan lifecycle events. Write a function that produces all the emails that should be sent, sorted chronologically, with the recipient and email type for each.

Algorithms & Data StructuresData ModelingSystem Design

Author's notes

Spent the first few minutes just making sure I understood the data model before touching any code.

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AI HintsAI Generated

Suggested Approach

Clarify the data model and assumptions (e.g., plan durations, time zones, email schedule semantics), then outline an algorithm that iterates over each user, computes relevant lifecycle events, applies offsets from the schedule to generate email records, and finally sorts all records by timestamp. Discuss trade-offs between precomputing events vs. on-the-fly generation, and consider scalability for large user bases.

Pro tip: Mention that you would handle time zones and daylight saving time consistently, and consider idempotency to avoid duplicate emails if the function is re-run—these are critical in production billing systems like Stripe.

1. Clarify requirements and assumptions

Ask about plan durations, how lifecycle events are defined (e.g., signup, expiry), the format of the schedule (offsets in days/hours), and whether emails should be generated for past or future events. Confirm sorting order and output format.

2. Define data structures

Model User (id, email, plan, signup_timestamp), Plan (duration, renewal behavior), and Schedule (email_type -> offset relative to event). Decide on a unified Email record (recipient, email_type, send_timestamp).

3. Design the algorithm

For each user, compute lifecycle events (e.g., signup, expiry, renewal). For each event, look up applicable email types and their offsets, compute send_timestamp = event_timestamp + offset, and create an Email record. Collect all records.

4. Sort and return

Sort the list of Email records by send_timestamp (ascending). If timestamps are equal, define a secondary sort (e.g., by user id or email type) for determinism. Return the sorted list.

5. Discuss edge cases and optimizations

Address edge cases: users with multiple plans, cancelled subscriptions, time zone handling, and large datasets. Suggest optimizations like batch processing, using a priority queue for merging pre-sorted per-user lists, or filtering by a time window.

Key Points to Mention

Time zone and daylight saving time handling: store timestamps in UTC and convert for display or sending.
Idempotency: ensure emails are not duplicated if the function is called multiple times (e.g., by tracking sent emails or using deterministic IDs).
Scalability: consider memory and time complexity; for large user bases, avoid loading all users into memory at once and use streaming or pagination.
Flexibility: design the schedule as a configuration that can be easily updated without code changes.
Edge cases: users with multiple subscriptions, plan upgrades/downgrades, and cancelled plans.
Testing: suggest unit tests for offset calculations, sorting, and edge cases like leap years or month-end offsets.

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.