System design interview question
"Design a caller-ID service. When an unknown number rings a user's phone, the app shows who is calling and whether the number is spam. The name data comes from other users' address books. Hundreds of millions of users, and the lookup has to complete before the phone stops ringing."
Whether the candidate confronts the privacy problem at the centre of the product. The names shown come from contacts uploaded by people who never asked the person being identified for permission. A candidate who designs the lookup path efficiently and never mentions this has missed what makes the question interesting — and would ship something with serious legal exposure.
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