← Instacart Interview Insights
Start by clarifying the four core operations (e.g., create account, deposit, withdraw, transfer) and non-functional requirements like consistency, availability, and scale. Then design a high-level architecture with services, data stores, and APIs, and drill into data models and concurrency control. Finally, discuss trade-offs (e.g., SQL vs NoSQL, locking vs optimistic concurrency) and how you would implement and test the system.
Pro tip: Emphasize idempotency and exactly-once semantics for operations like transfers, as financial systems must handle retries safely. Also, mention how you would monitor and audit transactions for compliance and debugging.
Ask questions to define the four operations, expected scale (users, transactions per second), consistency needs, and any regulatory constraints. Confirm whether the system is for a single bank or multiple institutions.
Outline the main components: API gateway, account service, transaction service, and data storage. Sketch how a request flows through the system for each operation.
Design the schema for accounts and transactions, choosing appropriate databases (e.g., relational for ACID, or distributed for scale). Explain how you would handle indexing and partitioning.
Describe how to prevent race conditions (e.g., using locks, optimistic concurrency, or serializable transactions) and ensure atomicity for transfers. Discuss idempotency keys to handle duplicate requests.
Compare design choices (e.g., SQL vs NoSQL, synchronous vs asynchronous processing) and justify your decisions. Outline a basic implementation plan and testing strategy, including failure scenarios.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.
Clarify the requirements first: are we validating or generating a password? Then outline a solution that balances correctness, efficiency, and security best practices, and discuss trade-offs. Finally, walk through the implementation with clean code and test cases.
Pro tip: Mention that password validation should avoid regex for complex rules due to readability and performance, and that generation should use a cryptographically secure random number generator. Also, consider edge cases like Unicode characters and password length limits.
Ask questions to understand the exact requirements: validation vs. generation, specific rules (length, character types), and any constraints (e.g., no repeating characters).
Describe a high-level algorithm, such as iterating through the password for validation or using a secure random generator for generation, and discuss time/space complexity.
Write clean, modular code with meaningful variable names, handling edge cases and using secure practices (e.g., constant-time comparison for validation).
Walk through test cases covering normal, edge, and invalid inputs, and explain how you would verify correctness and security.
Suggest potential optimizations or extensions, such as supporting configurable rules or integrating with a password strength library.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.
Clarify the problem constraints (e.g., operators allowed, integer vs floating-point, handling of spaces) and then propose a solution using two stacks (one for operands, one for operators) or a recursive descent parser. Walk through the algorithm step-by-step, handle operator precedence and parentheses, and analyze time and space complexity.
Pro tip: Mention that you would write unit tests for edge cases like negative numbers, multiple-digit numbers, and nested parentheses. Also, discuss how you would extend the solution to support additional operators or functions.
Ask about the allowed operators, number types (integer/float), handling of spaces, and whether parentheses are balanced. Confirm expected input size to discuss complexity.
Decide between two stacks (operands and operators) or recursive descent. Explain why one is preferred based on constraints (e.g., simplicity, extensibility).
Describe how to process tokens: push numbers onto operand stack, handle operators with precedence, and evaluate when encountering closing parenthesis or lower precedence operator.
Discuss handling of unary minus, multi-digit numbers, spaces, and invalid expressions. Mention error handling or assumptions.
State time and space complexity (O(n) time, O(n) space). Suggest test cases: simple expression, nested parentheses, negative numbers, and division by zero.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.