System design interview question
"Design a recommendation system. Given a user, produce a ranked list of items they are likely to want — products, videos, songs, whatever the catalogue is. A hundred million users, ten million items, and the recommendations must be produced in well under a hundred milliseconds."
the general recommendation architecture rather than one product's feed. The distinguishing content is: the retrieval-then-ranking funnel, why you cannot score every item, the cold-start problem for both users and items, and — the part most candidates skip — how you would know whether the system is any good.
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