Playlist / Guide Voting System (OOD)

Object-oriented design for a system of playlists holding guides, with add, upvote/downvote, and a getPlaylist that returns guides sorted by vote then timestamp. Extensibility follow-up points at the Strategy pattern. Requirements Model many playlists, each holding many guides. You choose all data structures and class boundaries. addGuide(guideId, userId, playlistId) — add a guide to a playlist (no return value). vote(guideId, userId, playlistId, vote) — register an upvote or downvote on a guide (no return value). getPlaylist(playlistId) — return all guides in a playlist sorted by vote count descending, ties broken by timestamp. Notes Standard shape: a Playlist owns Map<guideId, Guide>; each Guide tracks id, creator userId, creation timestamp, and a vote tally. Pin down vote semantics with the interviewer: can a user vote more than once, can they flip an upvote to a downvote? A per-guide Map<userId, voteValue> keeps voting idempotent. getPlaylist sorts on (votes desc, timestamp). When asked to support other orderings, pull the comparator out — the expected answer is the Strategy pattern (inject a sort strategy) rather than branching inside getPlaylist. Preparation Pre-write the class skeleton (Playlist, Guide, per-guide vote map) so interview time goes to the sort / extensibility discussion. Rehearse the Strategy extension aloud: a SortStrategy interface with byVotesThenTime, byRecency, etc., injected into getPlaylist.