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Plaid interview notes, page 3 of 3

Mid-sized

Most of these Plaid write-ups come from Software Engineers (14), then Machine Learning Engineers (3) and Frontend Engineers (2). The most reported rounds are the system design round (9), the technical phone screen (8), the product sense round (2) and the behavioral / leadership round (1).

21 interview notes · updated Jul 2026

Plaid·Software Engineer·Onsite - System Design / Architecture

Jul 2026
System design round at Plaid for a software engineering role, focused entirely on building an in-memory coupon service from scratch. Pretty intense for a single question but they kept piling on follow-ups until the time ran out.
  • Design an in-memory coupon service with addCoupon, redeem, and getRemaining operations. Walk through your data structure choices, explain how you'd achieve O(1) average-case performance, and analyze time and space complexity.
  • How would you handle edge cases like expired coupons, duplicate coupon codes, zero or negative discount values, and exceeding per-user or global redemption limits?
  • How would you make the redeem operation idempotent so retrying a failed request doesn't double-apply a coupon?
  • What edge cases around time would you worry about near a coupon's expiration, such as clock skew or daylight saving transitions?
  • How would you extend the service to support category-based restrictions on coupons, minimum spend thresholds, and bulk coupon input parsing?

“I went straight to hash maps and felt pretty good about it.”

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