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Design article voting and flip-tracking system

RipplingSoftware Engineer · Technical Screen
MediumSoftware EngineerTechnical ScreenSoftware Engineering Fundamentals

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This question tests your ability to design a stateful system for tracking user interactions (upvotes/downvotes) on content while maintaining an audit trail of user activity.

Design an Article Voting System

Design a backend service to manage voting on articles. The system must track the current score for each article and maintain a history of all voting actions performed by users.

Requirements

  1. Voting: Users can upvote or downvote an article. Each user can have only one active vote per article; casting a new vote replaces their previous one (e.g., changing from upvote to downvote).
  2. State: The system must provide the current net score (upvotes minus downvotes) for any given article.
  3. History: The system must maintain an audit log of every vote change, recording the user ID, article ID, vote value (+1, -1, or 0 for removed), and a timestamp.

Task

Design the class structure or data model and the interface methods to support the following:

  • vote(user_id, article_id, value)
  • get_score(article_id)
  • get_history(article_id)

Example

  • User A upvotes Article 1 (Score: 1)
  • User B downvotes Article 1 (Score: 0)
  • User A changes vote to downvote (Score: -1)

Considerations

  • How will you handle race conditions if multiple requests arrive simultaneously for the same article?
  • What data structures are most efficient for frequent score lookups vs. audit log storage?

Hints

Hint 1

Use a hash map to keep track of the current state of votes per user/article to ensure O(1) lookups for current scores.

Hint 2

Consider maintaining a secondary data structure specifically for the aggregate score that updates whenever a vote is cast to avoid re-calculating from the log.

Hint 3

Use a list or log-structured storage to append voting events chronologically to satisfy the history requirement.

Follow-up questions

  • How would you optimize the `get_score` operation if the articles receive millions of votes per second?
  • If you needed to implement a 'top 10 articles' leaderboard, which data structures would you add?
  • How would you ensure atomicity when updating the total score and the user's individual vote record simultaneously?