#933 - Number of Recent Calls

EasyQueue

Implement a RecentCounter class that counts the number of recent requests within a certain time frame.

• RecentCounter() – initializes the counter with zero requests.
• ping(t: number) – adds a new request at time t (strictly increasing) and returns the number of requests that have happened in the inclusive range [t - 3000, t].

Input	Output
Operations	Output
ping(1), ping(100), ping(3001), ping(3002)	[1, 2, 3, 3]

Solution Space

Try it

/**
 * Counts requests in a sliding 3000ms window using a queue.
 */
export class RecentCounter {
  private queue: number[] = [];
  private head = 0; // virtual dequeue pointer (avoids costly shift)

  ping(t: number): number {
    this.queue.push(t);

    // Remove timestamps outside the window
    while (this.queue[this.head] < t - 3000) {
      this.head++;
    }

    return this.queue.length - this.head;
  }
}

Approach: queue – enqueue each timestamp; dequeue (advance head pointer) all timestamps older than `t - 3000`. The remaining length is the answer.

Time: O(1) amortized per `ping` – each element is enqueued and dequeued at most once.

Space: O(n) – where n is the number of pings within any 3000ms window (at most 3001 entries).

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