Covers the systematic identification, analysis, and mitigation of edge cases and failures across code and user flows. Topics include methodically enumerating boundary conditions and unusual inputs such as empty inputs, single elements, large inputs, duplicates, negative numbers, integer overflow, circular structures, and null values; writing defensive code with input validation, null checks, and guard clauses; designing and handling error states including network timeouts, permission denials, and form validation failures; creating clear actionable error messages and informative empty states for users; methodical debugging techniques to trace logic errors, reproduce failing cases, and fix root causes; and testing strategies to validate robustness before submission. Also includes communicating edge case reasoning to interviewers and demonstrating a structured troubleshooting process.
MediumSystem Design
0 practiced
Design an idempotency strategy for a payment microservice that must avoid double-charges despite client retries. Requirements: support 1k TPS, idempotency keys with 24h TTL, multi-instance service, and minimal latency. Describe your data model, storage choice (in-memory vs durable), how to prevent races, eviction, and failure modes.
MediumTechnical
0 practiced
Write pytest tests that validate an API's pagination endpoint for edge cases: page number 0, negative page size, huge page size, last page with fewer items, concurrently changing data while paginating, and requesting a page beyond total results. Provide test structure, sample input, and assertions.
HardTechnical
0 practiced
After a regional failover, legitimate user traffic receives HTTP 429 responses intermittently. Create a forensic analysis plan to identify the root cause: rate limiter misconfiguration, token bucket state transfer across regions, client retry loops, DNS TTL issues, or traffic shaping. Propose immediate mitigations and long-term changes.
HardTechnical
0 practiced
Design a distributed rate limiter that supports bursts, persists counters safely across process restarts, and avoids integer overflow for clients that may perform up to 1M requests/day. Explain your algorithm, data layout, how to handle wraparound, clock skew across nodes, and tests to validate counter edge cases.
HardTechnical
0 practiced
Draft a post-incident review template specialized for edge-case failures. Specify required sections and artifacts (timeline, reproduction steps, escaped tests, monitoring gaps, configuration diffs, communication timeline), and explain how you'd ensure action items are owned, prioritized, and validated over time.
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