Number of Recent Calls

Leetcode Problem 933: Number of Recent Calls

Problem Summary

Implement a RecentCounter class that tracks the number of recent network requests within a 3,000-millisecond sliding window. It must support:

• RecentCounter() — Initializes the counter with no requests.
• ping(t) — Records a new request at time t milliseconds and returns the count of all requests in the inclusive range [t − 3000, t].

All calls to ping are made with strictly increasing timestamps.

Constraints:

• Timestamps are positive integers up to 1,000,000,000 milliseconds.
• At most 10,000 calls to ping will be made.

Techniques

• Design
• Queue
• Data Stream

Solution

class RecentCounter {
    constructor(
        private requests: number[] = []
    ) { }

    ping(t: number): number {
        let lowerBoundRequests = t - 3000
        this.requests.push(t)

        while (this.requests[0] < lowerBoundRequests) {
            this.requests.shift()
        }

        return this.requests.length
    }
}