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Design a Role-Based Password Validator
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1. Problem Statement
Implement a rate limiter. Start by asking any clarifying questions, then design and code an in-memory solution.
2. Live Coding Format
Work in the provided coding workspace while explaining your decisions to the live interviewer. Validation may use inline tests, examples, comments, or a verbal walkthrough.
3. Key Focus Areas
- 1Algorithm choice and justification (fixed window vs sliding log vs token bucket)
- 2Correct window-boundary enforcement
- 3In-memory state management per key
- 4Clock injection for testability
- 5Concurrency: race condition identification and mitigation strategy
- 6Handwritten tests: within-limit, at-limit, and over-limit cases
4. What Strong Candidates Should Demonstrate
- ✓Clarify the rate limiting contract: window type (fixed/sliding), granularity (per-user or global), and enforcement semantics (allow/deny vs consume/wait).
- ✓Choose and implement a correct in-memory algorithm — fixed window counter, sliding window log, or token bucket — and justify the tradeoff.
- ✓Discuss concurrency hazards (read-modify-write races) without needing to implement a full thread-safe solution in a 40-minute round.
- ✓Validate with handwritten test cases covering the window boundary and burst scenarios.
Want interactive feedback?
Practice this problem in the live coding workspace while the interviewer probes your clarification, implementation, trade-offs, and validation.
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