Created
September 3, 2012 20:40
-
-
Save jimwhite/3613264 to your computer and use it in GitHub Desktop.
Improved solution for Cedric's sliding window key problem.
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
// http://beust.com/weblog/2012/09/02/coding-challenge-a-sliding-window-map/ | |
import java.util.concurrent.PriorityBlockingQueue | |
public class SlidingWindowMap | |
{ | |
def queue | |
def windowWidthMillis | |
public SlidingWindowMap(Set<String> keys, int maxCount, long periodMs) | |
{ | |
queue = new PriorityBlockingQueue(keys.size() * maxCount, { a, b -> a[0].peek() <=> b[0].peek() } as Comparator) | |
def random = new Random() | |
// Seed the timestamps with random values that are earlier than the beginning of the window could be. | |
// Since System.currentTimeMillis() is a positive long we can use negative millions safely. | |
keys.each { key -> maxCount.times { queue.add([-random.nextInt(2**24), key]) } } | |
windowWidthMillis = periodMs | |
} | |
/** | |
* @return a key that has been used less than `maxCount` times during the | |
* past `periodMs` milliseconds or null if no such key exists. | |
*/ | |
public String getNextKey() | |
{ | |
// Get the key that was used first. | |
def keyrec = queue.poll() | |
if (keyrec) { | |
// Can we use it again? | |
if (keyrec[0] < System.currentTimeMillis() - windowWidthMillis) { | |
def key = keyrec[1] | |
queue.add ([System.currentTimeMillis(), key]) | |
return key | |
} | |
// No. Just put it back. | |
queue.add(keyrec) | |
} | |
return null | |
} | |
} |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment