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One natural approach to solve this problem is to use a queue data structure. A queue is perfect for this task because it works on a first-in-first-out (FIFO) principle. When a new request arrives, we add it to the queue. We also remove requests from the front of the queue that are older than 3000 milliseconds compared to the current time t. This allows us to keep only the requests within the last 3000 milliseconds in the queue. The number of such requests is simply the size of the queue after cleaning.
Time Complexity: Amortized O(1) because each request can only be removed once from the queue.
Space Complexity: O(W), where W is the maximum number of recent requests within 3000 milliseconds.
1#include <queue>
2using namespace std;
3
4class RecentCounter {
5 queue<int> q;
6public:
7 RecentCounter() {
8 }
9 int ping(int t) {
10 q.push(t);
11 while(q.front() < t - 3000) {
12 q.pop();
13 }
14 return q.size();
15 }
16};In this C++ implementation, we use the standard library queue to manage the requests. The ping method adds the new request time to the queue and removes old requests. The number of requests in the queue after removing outdated ones gives us the result.
An alternative approach to using a queue is to use a double-ended queue (deque). While similar to a queue, a deque allows us to add and remove elements from both ends, but in this problem, we'll only need the standard queue operations.
The logic remains the same: insert new request times to the back of the deque and remove outdated ones from the front. This keeps the deque maintaining only the relevant requests within the [t-3000, t] range.
Time Complexity: Amortized O(1) for each ping due to efficient pop and push operations.
Space Complexity: O(W), where W is size of the time window.
1from collections import deque
2
This Python solution utilizes deque to store the request timestamps, allowing constant time addition and removal as we maintain the sliding window.