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I've always wondered about this. I first read about this challenge in "Programming Collective Intelligence,"[0] the O'Reilly book from 2007 that drove me to become a professional programmer. It starts like this:

> Netflix is an online DVD rental company that lets people choose movies to be sent to their homes, and makes recommendations based on the movies that customers have previously rented.

It was a different and exciting time back then! I never finished that book but hope to some day... :)

[0] https://www.oreilly.com/library/view/programming-collective-...