1. Code

class RecentCounter:
    def __init__(self):
        self.queue = deque()

    def ping(self, t: int) -> int:
        self.queue.append(t) # This prevents the queue from being empty
        while self.queue[0] < t-3000:
            self.queue.popleft()
        return len(self.queue)

2. Result

        Runtime : 264 ms(99.10%), Memory usage : 19 MB(48.38%)
        (Runtime can be different by a system even if it is a same code.)

Check out the my GitHub repo for more info on the code. If you have questions, you can leave a reply on this post.