Debugging Testing and Optimization Questions

Core engineering skills for identifying, diagnosing, testing, and improving code correctness and performance. Covers approaches to finding and fixing bugs including reproducible test case construction, logging, interactive debugging, step through debugging, and root cause analysis. Includes testing strategies such as unit testing, integration testing, regression testing, test driven development, and designing tests for edge cases, boundary conditions, and negative scenarios. Describes performance optimization techniques including algorithmic improvements, data structure selection, reducing time and space complexity, memoization, avoiding unnecessary work, and parallelism considerations. Also covers measurement and verification methods such as benchmarking, profiling, complexity analysis, and trade off evaluation to ensure optimizations preserve correctness and maintainability.

EasyTechnical

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What is test driven development (TDD)? Describe a short workflow for adding a new feature using TDD in an agile sprint, including how you would balance failing tests, refactoring, and collaboration with product/design stakeholders.

MediumTechnical

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Implement a simple LRU cache in Java with get and put methods that both run in O(1) time. Provide brief unit test scenarios that verify eviction order, capacity behavior, and thread-safety assumptions (thread-safety not required to be implemented but must be discussed).

MediumTechnical

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Explain how you would profile and optimize a heavily used SQL JOIN that causes CPU spikes in the DB. Discuss rewriting queries, adding indexes, denormalization, materialized views, and when to move computation out of the DB.

HardTechnical

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A recent performance patch reduced average latency but increased p99 latency. How would you investigate and resolve this regression while preserving average-case gains? Describe analysis steps and possible code or system fixes.

EasyTechnical

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Explain how to use binary search over git commits to find the commit that introduced a regression. Describe the workflow, how to script it for automated bisecting, and how to handle non-deterministic or flaky failures during bisect.

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