Leetcode 3060. User Activities within Time Bounds

Design a system that records timestamped user events and answers queries about user activity within arbitrary start–end time bounds (e.g., count of events or distinct users) efficiently under large volumes of updates and queries. The core challenge is fast time-range counting with correct handling of duplicates and many online/offline queries, requiring time-indexed data structures or range-query algorithms (segment trees/Fenwick, ordered maps, sweep/Mo’s algorithm).