org.polymap.rhei.batik.engine.cp.SolutionQueueBuilder.java Source code

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Here is the source code for org.polymap.rhei.batik.engine.cp.SolutionQueueBuilder.java

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/* 
 * polymap.org
 * Copyright (C) 2013, Falko Brutigam. All rights reserved.
 *
 * This is free software; you can redistribute it and/or modify it
 * under the terms of the GNU Lesser General Public License as
 * published by the Free Software Foundation; either version 3.0 of
 * the License, or (at your option) any later version.
 *
 * This software 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
 * Lesser General Public License for more details.
 */
package org.polymap.rhei.batik.engine.cp;

import java.util.Collections;
import java.util.LinkedList;
import java.util.PriorityQueue;
import java.util.Queue;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import com.google.common.collect.MinMaxPriorityQueue;
import com.google.common.collect.Ordering;

import org.polymap.rhei.batik.engine.cp.ISolver.ScoredSolution;

/**
 * Factory for priority queues. Creates bound or unbound queues that have elements
 * ordered in reverse natural order.
 * 
 * @author <a href="http://www.polymap.de">Falko Brutigam</a>
 */
public class SolutionQueueBuilder {

    private static Log log = LogFactory.getLog(SolutionQueueBuilder.class);

    /**
     *
     * @param maxSize -1 signals that an unbound queue should be created. 
     * @return Newly created solution queue.
     */
    public static <T extends ScoredSolution> Queue<T> create(int maxSize) {
        if (maxSize < 0) {
            return new PriorityQueue<T>(1024, Ordering.natural().reverse());
        } else {
            return MinMaxPriorityQueue.orderedBy(Ordering.natural().reverse()).maximumSize(maxSize).create();
        }
    }

    /**
     * Unbound priority queue. Allows multiple elements with same score. 
     */
    static class ListBoundSolutionQueue<T extends ScoredSolution> extends LinkedList<T> {

        private int maxSize;

        public ListBoundSolutionQueue(int maxSize) {
            this.maxSize = maxSize;
        }

        @Override
        public boolean add(T elm) {
            int index = Collections.binarySearch(this, elm);
            if (index >= 0) {
                super.add(index, elm);
            } else {
                super.add(~index, elm);
            }
            if (size() == maxSize) {
                poll();
            }
            return true;
        }
    }

}