Which recommendation system technique did Netflix famously award $1 million to improve through the 'Netflix Prize' competition?

In today's competitive streaming landscape, major platforms like Netflix, Amazon Prime, and Disney+ rely heavily on sophisticated recommendation systems to keep viewers engaged and reduce churn. These AI-powered algorithms analyze viewing habits, preferences, and even production data to suggest content tailored to individual users. How well do you understand the technology behind what appears on your home screen?

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Collaborative filtering matrix factorization
Content-based neural networks
Contextual bandits algorithm
Bayesian personalization ranking