Implement an article voting tracker

Q: Implement an article voting tracker

This question evaluates a candidate's ability to design efficient stateful data structures and algorithms for tracking user votes, including correct handling of idempotent repeated votes, vote changes, deduplication, and retrieval of the most recent events.

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Question

Coding: Article Voting Tracker

Design and implement a data structure to track users’ votes (upvote/downvote) on articles.

Operations

Implement functions/methods with the following behavior:

vote(userId, articleId, voteType) where voteType ∈ {UP, DOWN}
- Track the user’s vote on the article.
- If the user repeats the same vote on the same article (e.g., UP then UP again), it should be counted only once (i.e., do not record a new vote event).
- If the user changes their vote on the same article (e.g., UP then DOWN, or DOWN then UP), it should be counted as a new vote event .
getLastVotes(userId)
- Return (or print) the user’s last 3 vote events , most recent first.
- Each returned event should include at least: (articleId, voteType, timestamp-or-order) .

Notes / constraints

Assume many users and articles.
The focus is on correct behavior and efficient operations.
Define and handle edge cases (e.g., user has < 3 vote events; unknown user).

Implement an article voting tracker

Overview

Coding: Article Voting Tracker

Operations

Notes / constraints

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