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Demo case file · Technical

Mid-size SaaS company

Senior Backend Engineer

Technology Technical Hard 60 min

This is a demo case file: a realistic example written from commonly known interview formats, not a real candidate's interview experience.

Questions asked

  1. Implement an LRU cache with O(1) get and put.
  2. Now make it safe to use from multiple threads at once. What are the trade-offs of your locking approach?
  3. Add a per-key time-to-live so entries expire. How do you avoid scanning the whole cache to find expired keys?

What to expect

One problem that kept growing in three stages, all in a shared editor with code that had to run. The interviewer cared about clean interfaces and tests more than speed. For the concurrency part they wanted me to compare one big lock against finer-grained locking and say when each is good enough.

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