Which pioneering recommendation algorithm, developed in the late 1990s, revolutionized online retail by introducing personalized product suggestions based on customer behavior?

The retail landscape has been transformed by AI-driven personalization algorithms that tailor shopping experiences to individual customers. These sophisticated systems analyze purchase history, browsing behavior, and even social media activity to create uniquely customized recommendations. But do you know which breakthrough innovation first brought mass personalization to online retail and fundamentally changed how we shop?

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Amazon's Item-to-Item Collaborative Filtering (1998)
Netflix's Cinematch Algorithm (2000)
Google's PageRank for Products (1999)
eBay's BidRecommender System (1997)