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Java example source code file (PriorityQueue.java)

This example Java source code file (PriorityQueue.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

arraylist, cloneable, counter, iterator, list, nosuchelementexception, numberformat, override, priorityqueue, serializable, string, stringbuilder, text, unsupportedoperationexception, util

The PriorityQueue.java Java example source code

/*
 *
 *  * Copyright 2015 Skymind,Inc.
 *  *
 *  *    Licensed under the Apache License, Version 2.0 (the "License");
 *  *    you may not use this file except in compliance with the License.
 *  *    You may obtain a copy of the License at
 *  *
 *  *        http://www.apache.org/licenses/LICENSE-2.0
 *  *
 *  *    Unless required by applicable law or agreed to in writing, software
 *  *    distributed under the License is distributed on an "AS IS" BASIS,
 *  *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  *    See the License for the specific language governing permissions and
 *  *    limitations under the License.
 *
 */

package org.deeplearning4j.berkeley;

import java.io.Serializable;
import java.text.NumberFormat;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.NoSuchElementException;

/**
 * A priority queue based on a binary heap.  Note that this implementation does
 * not efficiently support containment, removal, or element promotion
 * (decreaseKey) -- these methods are therefore not yet implemented.  It is a maximum
 * priority queue, so next() gives the highest-priority object.
 *
 * @author Dan Klein
 */
public class PriorityQueue<E> implements Iterator, Serializable, Cloneable, PriorityQueueInterface {
	private static final long serialVersionUID = 1L;
	int size;
	int capacity;
	List<E> elements;
	double[] priorities;

	protected void grow(int newCapacity) {
		List<E> newElements = new ArrayList(newCapacity);
		double[] newPriorities = new double[newCapacity];
		if (size > 0) {
			newElements.addAll(elements);
			System.arraycopy(priorities, 0, newPriorities, 0, priorities.length);
		}
		elements = newElements;
		priorities = newPriorities;
		capacity = newCapacity;
	}

	protected int parent(int loc) {
		return (loc - 1) / 2;
	}

	protected int leftChild(int loc) {
		return 2 * loc + 1;
	}

	protected int rightChild(int loc) {
		return 2 * loc + 2;
	}

	protected void heapifyUp(int loc) {
		if (loc == 0) return;
		int parent = parent(loc);
		if (priorities[loc] > priorities[parent]) {
			swap(loc, parent);
			heapifyUp(parent);
		}
	}

	protected void heapifyDown(int loc) {
		int max = loc;
		int leftChild = leftChild(loc);
		if (leftChild < size()) {
			double priority = priorities[loc];
			double leftChildPriority = priorities[leftChild];
			if (leftChildPriority > priority) max = leftChild;
			int rightChild = rightChild(loc);
			if (rightChild < size()) {
				double rightChildPriority = priorities[rightChild(loc)];
				if (rightChildPriority > priority
						&& rightChildPriority > leftChildPriority) max = rightChild;
			}
		}
		if (max == loc) return;
		swap(loc, max);
		heapifyDown(max);
	}

	protected void swap(int loc1, int loc2) {
		double tempPriority = priorities[loc1];
		E tempElement = elements.get(loc1);
		priorities[loc1] = priorities[loc2];
		elements.set(loc1, elements.get(loc2));
		priorities[loc2] = tempPriority;
		elements.set(loc2, tempElement);
	}

	protected void removeFirst() {
		if (size < 1) return;
		swap(0, size - 1);
		size--;
		elements.remove(size);
		heapifyDown(0);
	}

	/* (non-Javadoc)
	 * @see edu.berkeley.nlp.movingwindow.PriorityQueueInterface#hasNext()
	 */
	public boolean hasNext() {
		return !isEmpty();
	}

	/* (non-Javadoc)
	 * @see edu.berkeley.nlp.movingwindow.PriorityQueueInterface#next()
	 */
	public E next() {
		E first = peek();
		removeFirst();
		return first;
	}

	/* (non-Javadoc)
	 * @see edu.berkeley.nlp.movingwindow.PriorityQueueInterface#remove()
	 */
	public void remove() {
		throw new UnsupportedOperationException();
	}

	/* (non-Javadoc)
	 * @see edu.berkeley.nlp.movingwindow.PriorityQueueInterface#peek()
	 */
	public E peek() {
		if (size() > 0) return elements.get(0);
		throw new NoSuchElementException();
	}

	/* (non-Javadoc)
	 * @see edu.berkeley.nlp.movingwindow.PriorityQueueInterface#getPriority()
	 */
	public double getPriority() {
		if (size() > 0) return priorities[0];
		throw new NoSuchElementException();
	}

	/* (non-Javadoc)
	 * @see edu.berkeley.nlp.movingwindow.PriorityQueueInterface#size()
	 */
	public int size() {
		return size;
	}

	/* (non-Javadoc)
	 * @see edu.berkeley.nlp.movingwindow.PriorityQueueInterface#isEmpty()
	 */
	public boolean isEmpty() {
		return size == 0;
	}

	/* (non-Javadoc)
	 * @see edu.berkeley.nlp.movingwindow.PriorityQueueInterface#add(E, double)
	 */
	public boolean add(E key, double priority)
	{
		if (size == capacity) {
			grow(2 * capacity + 1);
		}
		elements.add(key);
		priorities[size] = priority;
		heapifyUp(size);
		size++;
		return true;
	}
	
	public void put(E key, double priority)
	{
		add(key, priority);
	}

	/**
	 * Returns a representation of the queue in decreasing priority order.
	 */
	@Override
	public String toString() {
		return toString(size(), false);
	}

	/**
	 * Returns a representation of the queue in decreasing priority order,
	 * displaying at most maxKeysToPrint elements and optionally printing
	 * one element per line.
	 *
	 * @param maxKeysToPrint
	 * @param multiline TODO
	 */
	public String toString(int maxKeysToPrint, boolean multiline) {
		PriorityQueue<E> pq = clone();
		StringBuilder sb = new StringBuilder(multiline ? "" : "[");
		int numKeysPrinted = 0;
		NumberFormat f = NumberFormat.getInstance();
		f.setMaximumFractionDigits(5);
		while (numKeysPrinted < maxKeysToPrint && pq.hasNext()) {
			double priority = pq.getPriority();
			E element = pq.next();
			sb.append(element == null ? "null" : element.toString());
			sb.append(" : ");
			sb.append(f.format(priority));
			if (numKeysPrinted < size() - 1) sb.append(multiline ? "\n" : ", ");
			numKeysPrinted++;
		}
		if (numKeysPrinted < size()) sb.append("...");
		if (!multiline) sb.append("]");
		return sb.toString();
	}

	/**
	 * Returns a counter whose keys are the elements in this priority queue, and
	 * whose counts are the priorities in this queue.  In the event there are
	 * multiple instances of the same element in the queue, the counter's count
	 * will be the sum of the instances' priorities.
	 *
	 * @return
	 */
	public Counter<E> asCounter() {
		PriorityQueue<E> pq = clone();
		Counter<E> counter = new Counter();
		while (pq.hasNext()) {
			double priority = pq.getPriority();
			E element = pq.next();
			counter.incrementCount(element, priority);
		}
		return counter;
	}

	/**
	 * Returns a clone of this priority queue.  Modifications to one will not
	 * affect modifications to the other.
	 */
	@Override
	public PriorityQueue<E> clone() {
		PriorityQueue<E> clonePQ = new PriorityQueue();
		clonePQ.size = size;
		clonePQ.capacity = capacity;
		clonePQ.elements = new ArrayList<E>(capacity);
		clonePQ.priorities = new double[capacity];
		if (size() > 0) {
			clonePQ.elements.addAll(elements);
			System.arraycopy(priorities, 0, clonePQ.priorities, 0, size());
		}
		return clonePQ;
	}

	public PriorityQueue() {
		this(15);
	}

	public PriorityQueue(int capacity) {
		int legalCapacity = 0;
		while (legalCapacity < capacity) {
			legalCapacity = 2 * legalCapacity + 1;
		}
		grow(legalCapacity);
	}

	public static void main(String[] args) {
		PriorityQueue<String> pq = new PriorityQueue();
		System.out.println(pq);
		pq.put("one", 1);
		System.out.println(pq);
		pq.put("three", 3);
		System.out.println(pq);
		pq.put("one", 1.1);
		System.out.println(pq);
		pq.put("two", 2);
		System.out.println(pq);
		System.out.println(pq.toString(2, false));
		while (pq.hasNext()) {
			System.out.println(pq.next());
		}
	}
}

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