/*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*/
/*
* Copyright (C) 2004
* & Matthias Schubert (schubert@dbs.ifi.lmu.de)
* & Zhanna Melnikova-Albrecht (melnikov@cip.ifi.lmu.de)
* & Rainer Holzmann (holzmann@cip.ifi.lmu.de)
*/
package weka.clusterers.forOPTICSAndDBScan.Utils;
import weka.core.RevisionHandler;
import weka.core.RevisionUtils;
import java.util.ArrayList;
import java.util.TreeMap;
/**
* <p>
* UpdateQueue.java <br/>
* Authors: Rainer Holzmann, Zhanna Melnikova-Albrecht, Matthias Schubert <br/>
* Date: Aug 27, 2004 <br/>
* Time: 5:36:35 PM <br/>
* $ Revision 1.4 $ <br/>
* </p>
*
* @author Matthias Schubert (schubert@dbs.ifi.lmu.de)
* @author Zhanna Melnikova-Albrecht (melnikov@cip.ifi.lmu.de)
* @author Rainer Holzmann (holzmann@cip.ifi.lmu.de)
* @version $Revision: 1.3 $
*/
public class UpdateQueue
implements RevisionHandler {
/**
* Used to store the binary heap
*/
private ArrayList queue;
/**
* Used to get efficient access to the stored Objects
*/
private TreeMap objectPositionsInHeap;
// *****************************************************************************************************************
// constructors
// *****************************************************************************************************************
/**
* Creates a new PriorityQueue (backed on a binary heap) with the ability to efficiently
* update the priority of the stored objects in the heap. The ascending (!) queue is
* dynamically growing and shrinking.
*/
public UpdateQueue() {
queue = new ArrayList();
objectPositionsInHeap = new TreeMap();
}
// *****************************************************************************************************************
// methods
// *****************************************************************************************************************
/**
* Adds a new Object to the queue
* @param priority The priority associated with the object (in this case: the reachability-distance)
* @param objectKey The key for this object
* @param o
*/
public void add(double priority, Object o, String objectKey) {
int objectPosition = 0;
if (objectPositionsInHeap.containsKey(objectKey)) {
objectPosition = ((Integer) objectPositionsInHeap.get(objectKey)).intValue();
if (((UpdateQueueElement) queue.get(objectPosition)).getPriority() <= priority) return;
queue.set(objectPosition++, new UpdateQueueElement(priority, o, objectKey));
} else {
queue.add(new UpdateQueueElement(priority, o, objectKey));
objectPosition = size();
}
heapValueUpwards(objectPosition);
}
/**
* Returns the priority for the object at the specified index
* @param index the index of the object
* @return priority
*/
public double getPriority(int index) {
return ((UpdateQueueElement) queue.get(index)).getPriority();
}
/**
* Restores the heap after inserting a new object
*/
private void heapValueUpwards(int pos) {
int a = pos;
int c = a / 2;
UpdateQueueElement recentlyInsertedElement = (UpdateQueueElement) queue.get(a - 1);
/** ascending order! */
while (c > 0 && getPriority(c - 1) > recentlyInsertedElement.getPriority()) {
queue.set(a - 1, queue.get(c - 1)); //shift parent-node down
objectPositionsInHeap.put(((UpdateQueueElement) queue.get(a - 1)).getObjectKey(), new Integer(a - 1));
a = c; //(c <= 0) => no parent-node remains
c = a / 2;
}
queue.set(a - 1, recentlyInsertedElement);
objectPositionsInHeap.put(((UpdateQueueElement) queue.get(a - 1)).getObjectKey(), new Integer(a - 1));
}
/**
* Restores the heap after removing the next element
*/
private void heapValueDownwards() {
int a = 1;
int c = 2 * a; //descendant
UpdateQueueElement updateQueueElement = (UpdateQueueElement) queue.get(a - 1);
if (c < size() && (getPriority(c) < getPriority(c - 1))) c++;
while (c <= size() && getPriority(c - 1) < updateQueueElement.getPriority()) {
queue.set(a - 1, queue.get(c - 1));
objectPositionsInHeap.put(((UpdateQueueElement) queue.get(a - 1)).getObjectKey(), new Integer(a - 1));
a = c;
c = 2 * a;
if (c < size() && (getPriority(c) < getPriority(c - 1))) c++;
}
queue.set(a - 1, updateQueueElement);
objectPositionsInHeap.put(((UpdateQueueElement) queue.get(a - 1)).getObjectKey(), new Integer(a - 1));
}
/**
* Returns the queue's size
* @return size
*/
public int size() {
return queue.size();
}
/**
* Tests, if the queue has some more elements left
* @return true, if there are any elements left, else false
*/
public boolean hasNext() {
return !(queue.size() == 0);
}
/**
* Returns the element with the lowest priority
* @return next element
*/
public UpdateQueueElement next() {
UpdateQueueElement next = (UpdateQueueElement) queue.get(0);
queue.set(0, queue.get(size() - 1));
queue.remove(size() - 1);
objectPositionsInHeap.remove(next.getObjectKey());
if (hasNext()) {
heapValueDownwards();
}
return next;
}
/**
* Returns the revision string.
*
* @return the revision
*/
public String getRevision() {
return RevisionUtils.extract("$Revision: 1.3 $");
}
}