How many patterns/rules were in the recommendation system — units, tens, hundreds?

The number of patterns and rules in a recommendation system can vary greatly depending on the complexity and scale of the project:

• In simple systems, there may be a few (single-digit) main rules, such as recommendations based on popularity or simple filters.
• In more complex systems, there are dozens of rules, including various heuristics, filters, personalization, and contextual factors.
• In large and mature systems, especially those employing machine learning and hybrid approaches, the number of rules and patterns can reach hundreds, combining many models and business logic.

For example, a recommendation system for an online store may use dozens of rules: from filtering by categories and price to analyzing user behavior and seasonal trends.