K-Repetitiveness Feature Value

Problem Overview

• Given a user's purchase history string, compute the k-repetitiveness feature: the number of substrings where some product category appears at least k times.
• Input: user_history (lowercase a-z, length 1 to 5e4) and integer k (1 to 5e4). Output: an integer count.
• Context: feature engineering for Amazon's recommendation system using purchase history data.
• This coding interview problem is an Amazon interviews interview question focused on string analysis and counting substrings.