Instacart Software Engineer Interview Experience — A Single CodeSignal OA Question With Five Escalating Follow-ups

The first step was an OA on CodeSignal. There was a lot of identity verification along the way — anti-cheating checks.

It was one question with multiple follow-ups, getting progressively harder. The OA email said you didn't need to finish everything, and honestly I don't think it's possible to finish it all — 90 minutes, 5 parts.

The problem gave you template code.

1. Implement account creation: createAccount(account_id) -> None
2. Implement payment and deposit methods
3. Return the top N accounts by number of transactions — this one was still fairly simple, you just had to keep each account's state and its transaction amounts up to date
4. Transfers between accounts, which can expire — and everything from the earlier parts still had to keep working correctly. This one was split into two steps: initializeTransaction(account1, account2, amount) -> transaction_id | None (return None if it can't be done), and accept(transaction_id) to accept the transaction, where you had to check whether it had already expired. Every method got passed the current timestamp.
5. Merge accounts. (Didn't get to this one.)

Ended up passing.