99클럽 코테 스터디 35일차 TIL (비기너)

<문제>

You have a RecentCounter class which counts the number of recent requests within a certain time frame.

Implement the RecentCounter class:

• RecentCounter() Initializes the counter with zero recent requests.

• int ping(int t) Adds a new request at time t, where t represents some time in milliseconds, and returns the number of requests that has happened in the past 3000 milliseconds (including the new request). Specifically, return the number of requests that have happened in the inclusive range [t - 3000, t].

It is guaranteed that every call to ping uses a strictly larger value of t than the previous call.

Example 1:

Input
["RecentCounter", "ping", "ping", "ping", "ping"]
[[], [1], [100], [3001], [3002]]
Output
[null, 1, 2, 3, 3]

Explanation
RecentCounter recentCounter = new RecentCounter();
recentCounter.ping(1);     // requests = [1], range is [-2999,1], return 1
recentCounter.ping(100);   // requests = [1, 100], range is [-2900,100], return 2
recentCounter.ping(3001);  // requests = [1, 100, 3001], range is [1,3001], return 3
recentCounter.ping(3002);  // requests = [1, 100, 3001, 3002], range is [2,3002], return 3

Constraints:

• 1 <= t <= 109

• Each test case will call ping with strictly increasing values of t.

• At most 104 calls will be made to ping.

<문제해설>

ping(t) 메서드는 t밀리세컨드에 ping이 들어왔음을 나타낸다. 이 때 [t-3000, t] 밀리세컨드 동안 들어온 ping의 갯수를 return하라!

<풀이>

class RecentCounter {

    ArrayDeque<Integer> pingTime = new ArrayDeque();

    //생성자
    public RecentCounter() {

    }


    public int ping(int t) {
        pingTime.offer(t);

        for(int i:pingTime){
            if(i < t - 3000){
                pingTime.poll();
            }
        }

        return pingTime.size();

    }
}

/**
 * Your RecentCounter object will be instantiated and called as such:
 * RecentCounter obj = new RecentCounter();
 * int param_1 = obj.ping(t);
 */

<접근방식>

1. 큐에 t를 집어넣었다. 그리고 t1<t2-3000 인 것들을 poll하고 남아있는 큐의 사이즈를 return 하였다.

2. 어려운 문제는 아니었다. 큐를 이용해서 풀었지만, 다른 자료구조를 통해서도 충분히 풀 수 있을 것 같다.

<마무리하며>

‘큐’ 자료구조가 많이 나오는 걸 보니, cs에서도 많이 사용되는 것 같다.