[LeetCode] Design Hit Counter

HitCounter.java

// Counts the number of hits in the past 5 minutes. 
//Each function accepts a timestamp parameter (in seconds granularity) and 
//you may assume that calls are being made to the system in chronological order 
//(ie, the timestamp is monotonically increasing). You may assume that the earliest timestamp starts at 1.

//It is possible that several hits arrive roughly at the same time.

public class HitCounter {
  int windowSize = 5 * 60; // since time interval is in seconds.
  Map<Long, Long> timeStampBucket = new HashMap<Long, Long>();
  long minStamp = 0;
  long totalHits = 0;

  public void logHits(long timeStamp) {
    cleanUp(timeStamp);
    if(timeStampBucket.containsKey(timeStamp)) {
      timeStampBucket.put(timeStamp, 1);
    }else {
      timeStampBucket.put(timeStamp, timeStampBucket.get(timeStamp) + 1); 
    }
    totalHits++;
  }

  public long getHits(long timeStamp) {
    cleanUp(timeStamp); // usually stays current timeStamp
    return totalHits;
  } 
  
  private void cleanUp(long timeStamp) {
    while(timeStamp - minStamp > windowSize) {
      if(timeStampBucket.containsKey(minStamp)) {
        totalHits -= timeStampBucket.get(minStamp);
        timeStampBucket.remove(minStamp++); 
      }
    }
  }
}