Mid-level interview questionAsked at Snap · interview write-up
Design a recommendation system for augmented-reality lenses in a camera app, including cold start for new lenses and new users.
Model answer
Two stages. Candidate generation from several sources: lenses near the user's history, trending lenses, lenses friends used, camera context. Then a ranker predicting try, capture and send. New lenses: content features like category, creator and a visual embedding, plus a small exploration slot. New users: regional popularity, adapting within the first sessions. Evaluate offline on a time split, then A/B test on sends, not just tries.
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