Time Range Event Counter

Different events stream into the system. Design a counter that supports recording events of various types and querying how many events of a given type occurred within an inclusive time range. Implement the EventCounter class:

• EventCounter() Initializes the counter.
• void receive(string eventType, int timestamp) Records that an event of eventType occurred at timestamp.
• int count(string eventType, int startTime, int endTime) Returns the number of events of eventType whose timestamp falls in [startTime, endTime] (both ends inclusive). You may assume timestamps passed to receive are non-decreasing across calls.

EventCounter ec = new EventCounter(); ec.receive("login", 1); ec.receive("login", 3); ec.receive("signup", 4); ec.receive("login", 7); ec.receive("login", 10); ec.count("login", 2, 8); // returns 2 (timestamps 3, 7) ec.count("login", 1, 10); // returns 4 (timestamps 1, 3, 7, 10) ec.count("signup", 1, 5); // returns 1 (timestamp 4) ec.count("signup", 5, 10); // returns 0 ec.count("logout", 1, 100); // returns 0 (event type never seen)