933. Number of Recent Calls

Problem Description

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

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 <= 10^9
• Each test case will call ping with strictly increasing values of t.
• At most 10^4 calls will be made to ping.

Python Solution

class RecentCounter:
    def __init__(self):
        self.requests = []
        
    def ping(self, t: int) -> int:
        self.requests.append(t)
        while self.requests[0] < t - 3000:
            self.requests.pop(0)
        return len(self.requests)

Java Solution

class RecentCounter {
    private Queue requests;
    
    public RecentCounter() {
        requests = new LinkedList<>();
    }
    
    public int ping(int t) {
        requests.offer(t);
        while (requests.peek() < t - 3000) {
            requests.poll();
        }
        return requests.size();
    }
}

C++ Solution

class RecentCounter {
private:
    queue requests;
    
public:
    RecentCounter() {}
    
    int ping(int t) {
        requests.push(t);
        while (requests.front() < t - 3000) {
            requests.pop();
        }
        return requests.size();
    }
};

JavaScript Solution

var RecentCounter = function() {
    this.requests = [];
};

/**
 * @param {number} t
 * @return {number}
 */
RecentCounter.prototype.ping = function(t) {
    this.requests.push(t);
    while (this.requests[0] < t - 3000) {
        this.requests.shift();
    }
    return this.requests.length;
};

C# Solution

public class RecentCounter {
    private Queue requests;
    
    public RecentCounter() {
        requests = new Queue();
    }
    
    public int Ping(int t) {
        requests.Enqueue(t);
        while (requests.Peek() < t - 3000) {
            requests.Dequeue();
        }
        return requests.Count;
    }
}