The duplicate check tripped me up for a second.
Start by clarifying the requirements and edge cases, then design a data model that efficiently supports account creation, deposits, and payments while tracking cumulative outgoing totals. Implement the solution using appropriate data structures, ensuring operations are correct and efficient, and discuss trade-offs.
Pro tip: Emphasize idempotency and error handling for payment operations, as financial systems require robustness against duplicate requests and failures. Also, consider thread-safety if the system is concurrent.
Ask questions to understand constraints: Are account IDs unique? What happens on insufficient funds? Should deposits be idempotent? Are there concurrency concerns?
Choose a data structure (e.g., hash map) to store accounts, mapping account ID to account object containing balance and cumulative outgoing total. Consider using a database for persistence if needed.
Write methods for createAccount (check duplicate), deposit (update balance), and processPayment (check balance, update balance and outgoing total). Ensure atomicity if concurrent.
Implement validation for negative amounts, non-existent accounts, insufficient funds, and duplicate account creation. Return appropriate errors or exceptions.
Write unit tests covering normal and edge cases. Discuss time/space complexity and potential optimizations (e.g., locking, transactions).
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.
Sorting on demand vs maintaining a sorted structure live.
Start by clarifying the schema and requirements, then outline a two-phase approach: aggregate outgoing payments per account, then sort by total descending and account ID ascending, and finally limit to N. Discuss trade-offs between in-memory sorting and using a heap for large datasets, and mention indexing strategies for efficiency.
Pro tip: Explicitly state your assumptions about the data (e.g., payment amounts are positive, account IDs are strings) and mention that you would validate them with the interviewer before writing code. This shows attention to detail and collaborative problem-solving.
Ask about the table structure, data types, and edge cases (e.g., null amounts, negative payments, accounts with no outgoing payments). Confirm the definition of 'outgoing payment' and whether N is a parameter.
Group by account ID and sum the outgoing payment amounts. Consider using a hash map or SQL GROUP BY, and discuss handling large datasets with partitioning or streaming.
Sort the aggregated results by total descending, and for ties, by account ID ascending. Explain that a stable sort or a custom comparator can achieve this.
If N is small relative to the number of accounts, use a min-heap of size N to avoid sorting all accounts. Discuss time and space complexity trade-offs.
Mention that an index on (account_id, amount) or a materialized view can speed up aggregation. For distributed systems, consider partitioning by account ID and using map-reduce style aggregation.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.
This is where things got interesting and also where I slowed down noticeably.
Start by clarifying the requirements and constraints, then propose a data model that tracks transfer states and balances. Discuss the trade-offs of immediate deduction vs. delayed credit, and outline the system components for handling acceptance, expiration, and consistency.
Pro tip: Emphasize idempotency and exactly-once processing to prevent double-spending or duplicate credits, and discuss how to handle race conditions between acceptance and expiration.
Ask questions to understand the scope: Is this for a single currency? What are the consistency guarantees? How should failures be handled? What are the notification requirements?
Propose a schema for transfers with states (PENDING, ACCEPTED, EXPIRED, CANCELLED) and timestamps. Include fields for source, target, amount, and expiration time.
Describe services: Transfer Service to initiate and manage transfers, Balance Service to handle deductions/credits, and a Scheduler for expiration. Consider using a message queue for asynchronous processing.
Discuss locking mechanisms (e.g., optimistic or pessimistic) to prevent race conditions. Ensure atomic operations for deduction and credit, and use idempotency keys to avoid duplicates.
Explain how to implement a timeout mechanism (e.g., scheduled jobs, TTL in database) and how to notify users of pending transfers and expirations.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.
Straightforward once the transfer registry was solid.
Start by clarifying the requirements and assumptions, such as the data model for transfers and accounts, and the expected behavior for invalid cases. Then outline a step-by-step algorithm that validates the accepting account, checks expiration, and updates balances atomically. Finally, discuss edge cases, error handling, and how to ensure idempotency and concurrency safety.
Pro tip: Emphasize idempotency and atomicity: use a unique transfer ID and database transactions with row-level locks to prevent double-crediting and race conditions. This shows you think about production reliability, not just the happy path.
Ask about the data model (e.g., transfer has targetAccountId, expiration timestamp, status), expected error responses, and whether the operation must be idempotent. Confirm if the accepting account is provided as input and how to identify it.
Outline checks: verify the accepting account matches the transfer's intended target, ensure the transfer hasn't expired (compare current time with expiration), and confirm the transfer is in a valid state (e.g., not already accepted or cancelled).
Describe using a database transaction to atomically update the transfer status and credit the account balance. Use row-level locking or optimistic concurrency control to prevent race conditions.
Define error responses for invalid account, expired transfer, already accepted transfer, and insufficient funds (if applicable). Discuss idempotency: if the same accept request is retried, return the same result without double-crediting.
Mention unit tests for each validation branch, integration tests for concurrency, and logging/metrics for failed attempts. Suggest adding alerts for unusual patterns like repeated expired transfer attempts.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.