362. Design Hit Counter

Problem §

Design a hit counter which counts the number of hits received in the past 5 minutes (i.e., the past 300 seconds).

Your system should accept a timestamp parameter (in seconds granularity), and you may assume that calls are being made to the system in chronological order (i.e., timestamp is monotonically increasing). Several hits may arrive roughly at the same time.

Implement the HitCounter class:

• HitCounter() Initializes the object of the hit counter system.
• void hit(int timestamp) Records a hit that happened at timestamp (in seconds). Several hits may happen at the same timestamp.
• int getHits(int timestamp) Returns the number of hits in the past 5 minutes from timestamp (i.e., the past 300 seconds).

We can assume that all timestamps input come in chronologically.

Examples §

Input

["HitCounter", "hit", "hit", "hit", "getHits", "hit", "getHits", "getHits"]  
[[], [1], [2], [3], [4], [300], [300], [301]]  

Output
[null, null, null, null, 3, null, 4, 3]

Explanation
HitCounter hitCounter = new HitCounter();
hitCounter.hit(1); // hit at timestamp 1.
hitCounter.hit(2); // hit at timestamp 2.
hitCounter.hit(3); // hit at timestamp 3.
hitCounter.getHits(4); // get hits at timestamp 4, return 3.
hitCounter.hit(300); // hit at timestamp 300.
hitCounter.getHits(300); // get hits at timestamp 300, return 4.
hitCounter.getHits(301); // get hits at timestamp 301, return 3.

Solutions §

We could use a deque for this question. For hit we just add to the right of the deque, and for getHit remove from the left until the first one on the left is within 300 seconds from the last, and return the size of the deque.

from collections import deque
 
class HitCounter:
    def __init__(self):
        self.counter = deque()
 
    def hit(self, timestamp):
        self.counter.append(timestamp)
    
    def getHit(self, timestamp):
        while len(self.counter) >= 0 and timestamp - self.counter[0] >= 300:
            self.counter.popleft()
        
        return len(self.counter)