Problem URL: Design hit counter

We will use a queue to store the timestamps of the hits. We will remove the timestamps that are older than 300 seconds. Then we will return the size of the queue.

class HitCounter:
    def __init__(self):
        self.hits = collections.deque()

    def hit(self, timestamp: int) -> None:
        self.hits.append(timestamp)

    def getHits(self, timestamp: int) -> int:
        while self.hits and timestamp - self.hits[0] >= 300:
            self.hits.popleft()
        return len(self.hits)

Time complexity: O(n)
Space complexity: O(n)