Coinbase Interview Questions — Page 21

Coinbase·Software Engineer·Technical Phone Screen

Jul 2026

Coinbase software engineering interview with a deep systems question about building an iterator library from scratch. Single question but it covered a lot of ground, from lazy combinators to invalidation semantics to unit tests. Felt more like a take-home that got crammed into a live session.

Design and implement a full iterator library supporting range(start, end, step) with forward and backward traversal, inclusive and exclusive endpoints, negative steps, and overflow-safe termination. Include lazy combinators (map, filter, zip, take, drop, chain) each using O(1) space, a PeekableIterator with peek() and hasNext(), and discuss whether reset()/rewind() is feasible without materializing the sequence. Also define iterator invalidation rules when the underlying collection mutates, and write unit tests for edge cases like zero step, empty ranges, very large ranges, and negative steps.

“This was a lot.”

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Coinbase·Software Engineer·Online Assessment (OA)

Jul 2026

Coinbase SWE online assessment, the whole thing was a single evolving in-memory database problem split into four parts. Each part built on the last so you couldn't really skip ahead or ignore earlier code. Pretty classic OA format but the TTL and backup/restore parts had enough edge cases to keep you on your toes.

Implement a basic in-memory key-value store with put and get operations, where each record has a string key, string value, and integer timestamp. Multiple writes to the same key should return the most recent value.
Extend the database to support a scan operation that returns all key-value pairs whose keys share a given prefix, sorted lexicographically.
Add optional TTL support to the put operation so entries expire after a given number of seconds. Get and scan should not return expired entries.
Add backup and restore functionality. Backup should capture all non-expired entries at a given timestamp and return an ID. Restore should bring the database back to that snapshot, with TTLs adjusted so remaining lifetime is preserved relative to the restore time.

“Straightforward enough.”

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Coinbase·Software Engineer·Technical Phone Screen

Jul 2026

Coinbase SWE interview with a dynamic programming problem that looked straightforward but had enough moving parts to keep you honest. The transaction fee twist changes the whole approach and they wanted proof of correctness too, not just working code.

Given an array of daily stock prices and a fixed fee applied on each sale, find the maximum profit you can make with unlimited buy-sell transactions. They want an O(n) solution, a correctness argument, and handling for edge cases like empty input or prices that only go down.

“The fee-per-sell detail is what makes this not just a standard stock problem.”

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Coinbase·Software Engineer·Technical Phone Screen

Jul 2026

Coinbase software engineering interview focused entirely on designing a mini in-memory database with cursor-based pagination. The problem sounds straightforward but the follow-ups get into some genuinely tricky territory around cursor encoding and duplicate scores.

Design an in-memory database that stores rows with an id, score, and payload, and implement a query that returns all rows where score is at or above a given minimum, sorted by score ascending then id ascending.
Implement cursor-based pagination for the query above: the client sends a cursor representing the last row seen, and the server returns the next page of results plus a nextCursor, or null if there are nothing left.
How do you encode the cursor so it is stable and unambiguous across requests?
When many rows share the same score, how do you ensure no rows are duplicated or skipped across page boundaries?
What is the time complexity of your solution, and how would you scale it for datasets with up to a million rows?

“The sorting part is easy enough, composite sort on score then id.”

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Coinbase·Data Scientist·Technical Phone Screen

Jul 2026

Coinbase data science interview with a product estimation question built around a real marketing scenario. Pretty open-ended, which I wasn't fully prepared for.

A crypto company runs a Super Bowl ad showing only a QR code. Viewers who scan it and complete sign-up get a $15 coupon. Estimate the total number of successful sign-ups from that campaign.

“I started with Super Bowl viewership, which felt solid ground, then immediately got tangled trying to estimate scan rates because I kept second-guessing myself on how many people actually have their phone out while watching.”

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Coinbase·Frontend Engineer·Onsite - System Design / Architecture

Jul 2026

Staff-level frontend interview at Coinbase centered around a deep technical presentation of a past project. You draw an architecture diagram live and walk through it with senior engineers asking follow-ups the whole way. Pretty intense if your project doesn't have enough meat on it.

Walk us through a past project you owned, including the business problem, your architecture decisions, and the measurable impact you delivered.
What were the major technical tradeoffs you made during the project, and would you make the same calls again?
Describe a significant failure, incident, or constraint you hit during the project and how you handled it.
How did you collaborate with other teams, and how did you handle disagreements or misaligned priorities?
If you could redo this project from scratch, what would you change about the architecture or your approach?

“This is basically the whole interview.”

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Coinbase·Software Engineer·Technical Phone Screen

Jul 2026

Coinbase SWE interview with a meaty in-memory system design coding problem. The whole session was basically one big question about building a task management system from scratch, with layers added as you went. Felt like a LeetCode-style OOP problem but with enough edge cases to keep you honest.

Design and implement an in-memory task management system supporting task CRUD, priority-based listing, user quotas, task assignment with TTL, and completion/expiration rules.
Return the top N tasks by priority, and also return the top N tasks by priority whose name contains a given substring.
Implement task assignment with TTL: assign a task to a user at a given startTime with a duration, enforce user quota limits on active assignments, and support listing a user's active assignments at time t.
Implement task completion: allow completing a task for a user at time t, prevent completing an expired assignment, and when multiple active assignments exist for the same user-task pair, complete the one with the earliest startTime.

“This is one of those problems that looks like a data structures question but is really about keeping your design clean under pressure.”

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Coinbase·Software Engineer·Technical Phone Screen

Jul 2026

Coinbase software engineering interview that was basically one long design problem broken into four escalating parts. The scope kept expanding and by the end I was sketching out merge logic for user histories which I did not see coming at all.

Design an in-memory banking system with account creation, deposits, and transfers between users. How do you handle error cases like unknown users or insufficient funds?
Add a method to return the top K accounts ranked by total outgoing spend. What data structure do you use and how do you define tie-breaking?
Extend the system to support scheduled future payments with unique IDs, cancellation, and a mechanism to advance time and execute due payments.
Implement a mergeUsers operation that combines two accounts, preserves full transaction history, and handles any scheduled payments that involved the source user after the merge.

“Pretty standard starting point but I fumbled the error handling spec a bit.”

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Coinbase·Data Scientist·Onsite - Product Sense / Strategy

Jul 2026

Coinbase DS interview with two meaty case questions back to back, one on campaign measurement and one on whether to list a new trading pair. No fluff, just open-ended frameworks with a lot of moving parts. Felt like a take-home that got turned into a live conversation.

You ran a 4-week paid marketing campaign across multiple channels. How would you evaluate whether it succeeded?
How would you compare campaign performance fairly across channels like Search, Social, and Affiliates?
What guardrail metrics would you watch during a marketing campaign, and why?
Product wants to list a new trading pair. Walk me through how you'd decide whether to launch it.
How would you evaluate liquidity and market quality for a newly listed trading pair?
After launching a new trading pair, what metrics would define success and how would you monitor them?

“I started with incremental funded accounts as the primary metric because raw signups are too easy to game and revenue takes too long to materialize in a 4-week window.”

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Coinbase·Data Scientist·Online Assessment (OA)

Jul 2026

Coinbase Data Scientist aptitude screen, the timed kind where you have 50 questions and 15 minutes and basically have to triage on the fly. Mix of number sequences, pattern recognition, and grammar. Nothing conceptually hard but the clock is the whole challenge.

What is the next number in the sequence 3, 6, 12, 24, ___?
A repeating symbol pattern (triangle, square, circle) cycles in order. Which symbol appears in the 10th position?
Fill in the blank: 'She postponed the launch because she ____ the data were incomplete.' Choose the correct verb form from the options given.

“Each term doubles.”

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