933. Number of Recent Calls (Easy)


Write a class RecentCounter to count recent requests.

It has only one method: ping(int t), where t represents some time in milliseconds.

Return the number of pings that have been made from 3000 milliseconds ago until now.

Any ping with time in [t - 3000, t] will count, including the current ping.

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


Example 1:

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



  1. Each test case will have at most 10000 calls to ping.
  2. Each test case will call ping with strictly increasing values of t.
  3. Each call to ping will have 1 <= t <= 10^9.



class RecentCounter {
    private Queue<Integer> queue;

    public RecentCounter() {
        // We can use PriorityQueue if incoming pings are out of order
        // Since problem already clarified the every ping is larger than previous,
        // no need to sort them and computed overhead.
        queue = new LinkedList<>();

    public int ping(int t) {

        // poll the expired ping out of the queue and conserve the space
        while (queue.peek() < t - 3000) {

        return queue.size();

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