The base version of this problem isn't bad, just simulate debits and track balances.
Start by clarifying the requirements and edge cases, then propose a solution that processes transactions sequentially, updating balances in a consistent order. Emphasize correctness, efficiency, and handling of edge cases like insufficient funds and concurrent transactions.
Pro tip: Discuss how you would handle concurrency and idempotency, as these are critical in financial systems like Stripe. Mentioning database transactions or locking mechanisms can demonstrate maturity.
Ask questions to understand the data model, transaction ordering, and expected behavior for edge cases (e.g., negative amounts, multiple transactions from same account).
Choose appropriate data structures to store account balances (e.g., hash map) and process transactions efficiently.
Iterate through transactions, attempt to deduct from source account, then platform account if needed, and reject if both fail. Update balances accordingly.
Consider scenarios like insufficient funds in both accounts, invalid account IDs, and concurrent transactions. Discuss how to ensure atomicity and consistency.
State the time and space complexity of your solution, typically O(n) time and O(m) space where n is number of transactions and m is number of accounts.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.