Implement image carousel with comments and upvotes
Company: DoorDash
Role: Software Engineer
Category: Coding & Algorithms
Difficulty: medium
Interview Round: Onsite
Implement an image carousel that supports:
1) cycling forward/backward and autoplay with a configurable interval;
2) a per-image comment thread with create/read/edit/delete;
3) upvoting/downvoting comments and returning the top-k comments per image ordered by score, breaking ties by recency. Design the data structures to support add/delete comment, update vote, and query top-k efficiently at scale (up to 10^5 images and 10^6 comments across images). Specify the time/space complexities, the APIs you would expose (including pagination of comments), and how you would prevent double-counting when a user rapidly toggles votes.
Overview: This question evaluates a candidate's ability to design scalable data structures and efficient algorithms for interactive features, including API design, pagination, and consistency/concurrency handling for upvotes and per-image comment threads.
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