System design interview question
"Design a service that identifies a song from a short recording made on a phone — in a bar, with people talking, the phone in someone's pocket, ten seconds of audio starting from an arbitrary point in the track. Catalogue of a hundred million songs, answer in under a second."
Whether the candidate can turn a similarity problem into an exact-match lookup. Comparing audio to a hundred million songs is hopeless; the entire design hinges on constructing a fingerprint that is robust to noise, invariant to the starting offset, and — crucially — usable as a hash key so the search becomes a hash lookup rather than a comparison.
On Practick another engineer interviews you live for 60 minutes on a question from this bank. They have the full interviewer guide beside the call: the answers to your clarifying questions, the numbers to hand out, a ladder of follow-ups and a scoring rubric. You get the model solution once the session settles. It is free: interview someone for an hour and you have earned your own.
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