362. Design Hit Counter

Design a hit counter which counts the number of hits received in the past 5 minutes (i.e., the past 300 seconds).

Your system should accept a timestamp parameter (in seconds granularity), and you may assume that calls are being made to the system in chronological order (i.e., timestamp is monotonically increasing). Several hits may arrive roughly at the same time.

Implement the HitCounter class:

• HitCounter() Initializes the object of the hit counter system.
• void hit(int timestamp) Records a hit that happened at timestamp (in seconds). Several hits may happen at the same timestamp.
• int getHits(int timestamp) Returns the number of hits in the past 5 minutes from timestamp (i.e., the past 300 seconds).

class HitCounter {
    multiset<int> s;
public:
    /** Initialize your data structure here. */
    HitCounter() {}

    /** Record a hit.
        @param timestamp - The current timestamp (in seconds granularity). */
    void hit(int timestamp) {
        s.insert(timestamp);
    }

    /** Return the number of hits in the past 5 minutes.
        @param timestamp - The current timestamp (in seconds granularity). */
    int getHits(int timestamp) {
        auto f = s.upper_bound(timestamp - 300);
        auto t = s.upper_bound(timestamp);
        return distance(f, t);
    }
};

/**
 * Your HitCounter object will be instantiated and called as such:
 * HitCounter* obj = new HitCounter();
 * obj->hit(timestamp);
 * int param_2 = obj->getHits(timestamp);
 */