These are LLD questions of the kind Google actually asks — the patterns reported from Google's AI-engineering rounds, where design trade-offs, scale and failure modes matter as much as definitions. Treat this page as a mock interview: say every answer out loud before revealing it. If one surprises you, the lesson behind it is linked at the bottom.
Google LLD concept questions
Google's LLD interviews often reward minimal, clean abstractions over exhaustive pattern usage. Design a simple in-memory key-value cache with an LRU eviction policy.
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Why might Google interviewers push back if your Cache class exposes both get/put AND direct access to its internal linked list?
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Interviewer: 'now make the cache thread-safe, and support a TTL (time-to-live) per entry.' What changes, and what stays the same?
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How to use this page: Google rarely asks something you've never seen — they ask a standard LLD concept and then push one level deeper ("why?", "what would you do if..."). Master the concept in the LLD course lessons, and the follow-up stops being scary.
Keep practising: SOLID Principles, Strategy Pattern, Design a Parking Lot and UML Diagrams cover what most Google LLD rounds test.