/*
	* Copyright (C) 2003-2019 Paolo Boldi and Sebastiano Vigna
	*
	* 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 it.unimi.dsi.fastutil.longs;
import it.unimi.dsi.fastutil.ints.IntArrays;
import java.util.NoSuchElementException;
A type-specific array-based semi-indirect priority queue.

Instances of this class use as reference list a reference array, which must be provided to each constructor, and represent a priority queue using a backing array of integer indices—all operations are performed directly on the array. The array is enlarged as needed, but it is never shrunk. Use the trim() method to reduce its size, if necessary. 

This implementation is extremely inefficient, but it is difficult to beat
when the size of the queue is very small. Moreover, it allows to enqueue
several time the same index, without limitations.
/**
 * A type-specific array-based semi-indirect priority queue.
 *
 * <p>
 * Instances of this class use as reference list a <em>reference array</em>,
 * which must be provided to each constructor, and represent a priority queue
 * using a backing array of integer indices&mdash;all operations are performed
 * directly on the array. The array is enlarged as needed, but it is never
 * shrunk. Use the {@link #trim()} method to reduce its size, if necessary.
 *
 * <p>
 * This implementation is extremely inefficient, but it is difficult to beat
 * when the size of the queue is very small. Moreover, it allows to enqueue
 * several time the same index, without limitations.
 */
public class LongArrayIndirectPriorityQueue implements LongIndirectPriorityQueue {
	
The reference array. /** The reference array. */
	protected long refArray[];
	
The backing array. /** The backing array. */
	protected int array[] = IntArrays.EMPTY_ARRAY;
	
The number of elements in this queue. /** The number of elements in this queue. */
	protected int size;
	
The type-specific comparator used in this queue. /** The type-specific comparator used in this queue. */
	protected LongComparator c;
	
The first index, cached, if firstIndexValid is true. /** The first index, cached, if {@link #firstIndexValid} is true. */
	protected int firstIndex;
	
Whether firstIndex contains a valid value. /** Whether {@link #firstIndex} contains a valid value. */
	protected boolean firstIndexValid;
	
Creates a new empty queue without elements with a given capacity and
comparator.
Params:
refArray – 
           the reference array.
capacity – 
           the initial capacity of this queue.
c –  the comparator used in this queue, or null for the natural order./**
	 * Creates a new empty queue without elements with a given capacity and
	 * comparator.
	 *
	 * @param refArray
	 *            the reference array.
	 * @param capacity
	 *            the initial capacity of this queue.
	 * @param c
	 *            the comparator used in this queue, or {@code null} for the natural
	 *            order.
	 */
	public LongArrayIndirectPriorityQueue(long[] refArray, int capacity, LongComparator c) {
		if (capacity > 0)
			this.array = new int[capacity];
		this.refArray = refArray;
		this.c = c;
	}
	
Creates a new empty queue with given capacity and using the natural order.
Params:
refArray – 
           the reference array.
capacity – 
           the initial capacity of this queue./**
	 * Creates a new empty queue with given capacity and using the natural order.
	 *
	 * @param refArray
	 *            the reference array.
	 * @param capacity
	 *            the initial capacity of this queue.
	 */
	public LongArrayIndirectPriorityQueue(long[] refArray, int capacity) {
		this(refArray, capacity, null);
	}
	
Creates a new empty queue with capacity equal to the length of the reference
array and a given comparator.
Params:
refArray – 
           the reference array.
c –  the comparator used in this queue, or null for the natural order./**
	 * Creates a new empty queue with capacity equal to the length of the reference
	 * array and a given comparator.
	 *
	 * @param refArray
	 *            the reference array.
	 * @param c
	 *            the comparator used in this queue, or {@code null} for the natural
	 *            order.
	 */
	public LongArrayIndirectPriorityQueue(long[] refArray, LongComparator c) {
		this(refArray, refArray.length, c);
	}
	
Creates a new empty queue with capacity equal to the length of the reference
array and using the natural order.
Params:
refArray – 
           the reference array./**
	 * Creates a new empty queue with capacity equal to the length of the reference
	 * array and using the natural order.
	 * 
	 * @param refArray
	 *            the reference array.
	 */
	public LongArrayIndirectPriorityQueue(long[] refArray) {
		this(refArray, refArray.length, null);
	}
	
Wraps a given array in a queue using a given comparator.

The queue returned by this method will be backed by the given array.
Params:
refArray – 
           the reference array.
a –  an array of indices into refArray.
size – 
           the number of elements to be included in the queue.
c –  the comparator used in this queue, or null for the natural order./**
	 * Wraps a given array in a queue using a given comparator.
	 *
	 * <p>
	 * The queue returned by this method will be backed by the given array.
	 *
	 * @param refArray
	 *            the reference array.
	 * @param a
	 *            an array of indices into {@code refArray}.
	 * @param size
	 *            the number of elements to be included in the queue.
	 * @param c
	 *            the comparator used in this queue, or {@code null} for the natural
	 *            order.
	 */
	public LongArrayIndirectPriorityQueue(final long[] refArray, final int[] a, int size, final LongComparator c) {
		this(refArray, 0, c);
		this.array = a;
		this.size = size;
	}
	
Wraps a given array in a queue using a given comparator.

The queue returned by this method will be backed by the given array.
Params:
refArray – 
           the reference array.
a –  an array of indices into refArray.
c –  the comparator used in this queue, or null for the natural order./**
	 * Wraps a given array in a queue using a given comparator.
	 *
	 * <p>
	 * The queue returned by this method will be backed by the given array.
	 *
	 * @param refArray
	 *            the reference array.
	 * @param a
	 *            an array of indices into {@code refArray}.
	 * @param c
	 *            the comparator used in this queue, or {@code null} for the natural
	 *            order.
	 */
	public LongArrayIndirectPriorityQueue(final long[] refArray, final int[] a, final LongComparator c) {
		this(refArray, a, a.length, c);
	}
	
Wraps a given array in a queue using the natural order.

The queue returned by this method will be backed by the given array.
Params:
refArray – 
           the reference array.
a –  an array of indices into refArray.
size – 
           the number of elements to be included in the queue./**
	 * Wraps a given array in a queue using the natural order.
	 *
	 * <p>
	 * The queue returned by this method will be backed by the given array.
	 *
	 * @param refArray
	 *            the reference array.
	 * @param a
	 *            an array of indices into {@code refArray}.
	 * @param size
	 *            the number of elements to be included in the queue.
	 */
	public LongArrayIndirectPriorityQueue(final long[] refArray, final int[] a, int size) {
		this(refArray, a, size, null);
	}
	
Wraps a given array in a queue using the natural order.

The queue returned by this method will be backed by the given array.
Params:
refArray – 
           the reference array.
a –  an array of indices into refArray./**
	 * Wraps a given array in a queue using the natural order.
	 *
	 * <p>
	 * The queue returned by this method will be backed by the given array.
	 *
	 * @param refArray
	 *            the reference array.
	 * @param a
	 *            an array of indices into {@code refArray}.
	 */
	public LongArrayIndirectPriorityQueue(final long[] refArray, final int[] a) {
		this(refArray, a, a.length);
	}
	
Returns the index (in array) of the smallest element. /** Returns the index (in {@link #array}) of the smallest element. */

	private int findFirst() {
		if (firstIndexValid)
			return this.firstIndex;
		firstIndexValid = true;
		int i = size;
		int firstIndex = --i;
		long first = refArray[array[firstIndex]];
		if (c == null)
			while (i-- != 0) {
				if (((refArray[array[i]]) < (first)))
					first = refArray[array[firstIndex = i]];
			}
		else
			while (i-- != 0) {
				if (c.compare(refArray[array[i]], first) < 0)
					first = refArray[array[firstIndex = i]];
			}
		return this.firstIndex = firstIndex;
	}
	
Returns the index (in array) of the largest element. /** Returns the index (in {@link #array}) of the largest element. */

	private int findLast() {
		int i = size;
		int lastIndex = --i;
		long last = refArray[array[lastIndex]];
		if (c == null) {
			while (i-- != 0)
				if (((last) < (refArray[array[i]])))
					last = refArray[array[lastIndex = i]];
		} else {
			while (i-- != 0)
				if (c.compare(last, refArray[array[i]]) < 0)
					last = refArray[array[lastIndex = i]];
		}
		return lastIndex;
	}
	protected final void ensureNonEmpty() {
		if (size == 0)
			throw new NoSuchElementException();
	}
	
Ensures that the given index is a firstIndexValid reference.
Params:
index – 
           an index in the reference array.
Throws:
IndexOutOfBoundsException – 
            if the given index is negative or larger than the reference array
            length./**
	 * Ensures that the given index is a firstIndexValid reference.
	 *
	 * @param index
	 *            an index in the reference array.
	 * @throws IndexOutOfBoundsException
	 *             if the given index is negative or larger than the reference array
	 *             length.
	 */
	protected void ensureElement(final int index) {
		if (index < 0)
			throw new IndexOutOfBoundsException("Index (" + index + ") is negative");
		if (index >= refArray.length)
			throw new IndexOutOfBoundsException(
					"Index (" + index + ") is larger than or equal to reference array size (" + refArray.length + ")");
	}
	
{@inheritDoc}

Note that for efficiency reasons this method will not throw an exception when x is already in the queue. However, the queue state will become inconsistent and the following behaviour will not be predictable. /**
	 * {@inheritDoc}
	 *
	 * <p>
	 * Note that for efficiency reasons this method will <em>not</em> throw an
	 * exception when {@code x} is already in the queue. However, the queue state
	 * will become inconsistent and the following behaviour will not be predictable.
	 */
	@Override

	public void enqueue(int x) {
		ensureElement(x);
		if (size == array.length)
			array = IntArrays.grow(array, size + 1);
		if (firstIndexValid) {
			if (c == null) {
				if (((refArray[x]) < (refArray[array[firstIndex]])))
					firstIndex = size;
			} else if (c.compare(refArray[x], refArray[array[firstIndex]]) < 0)
				firstIndex = size;
		} else
			firstIndexValid = false;
		array[size++] = x;
	}
	@Override
	public int dequeue() {
		ensureNonEmpty();
		final int firstIndex = findFirst();
		final int result = array[firstIndex];
		if (--size != 0)
			System.arraycopy(array, firstIndex + 1, array, firstIndex, size - firstIndex);
		firstIndexValid = false;
		return result;
	}
	@Override
	public int first() {
		ensureNonEmpty();
		return array[findFirst()];
	}
	@Override
	public int last() {
		ensureNonEmpty();
		return array[findLast()];
	}
	@Override
	public void changed() {
		ensureNonEmpty();
		firstIndexValid = false;
	}
	
{@inheritDoc}

Note that for efficiency reasons this method will not throw an exception when index is not in the queue. /**
	 * {@inheritDoc}
	 *
	 * <p>
	 * Note that for efficiency reasons this method will <em>not</em> throw an
	 * exception when {@code index} is not in the queue.
	 */
	@Override
	public void changed(int index) {
		ensureElement(index);
		if (index == firstIndex)
			firstIndexValid = false;
	}
	
Signals the queue that all elements have changed. /** Signals the queue that all elements have changed. */
	@Override
	public void allChanged() {
		firstIndexValid = false;
	}
	@Override
	public boolean remove(int index) {
		ensureElement(index);
		final int[] a = array;
		int i = size;
		while (i-- != 0)
			if (a[i] == index)
				break;
		if (i < 0)
			return false;
		firstIndexValid = false;
		if (--size != 0)
			System.arraycopy(a, i + 1, a, i, size - i);
		return true;
	}
	
Writes in the provided array the front of the queue, that is, the
set of indices whose elements have the same priority as the top.
Params:
a – 
           an array whose initial part will be filled with the frnot (must be
           sized as least as the heap size).
Returns:
the number of elements of the front./**
	 * Writes in the provided array the <em>front</em> of the queue, that is, the
	 * set of indices whose elements have the same priority as the top.
	 * 
	 * @param a
	 *            an array whose initial part will be filled with the frnot (must be
	 *            sized as least as the heap size).
	 * @return the number of elements of the front.
	 */
	@Override
	public int front(int[] a) {
		final long top = refArray[array[findFirst()]];
		int i = size, c = 0;
		while (i-- != 0)
			if (((top) == (refArray[array[i]])))
				a[c++] = array[i];
		return c;
	}
	@Override
	public int size() {
		return size;
	}
	@Override
	public void clear() {
		size = 0;
		firstIndexValid = false;
	}
	
Trims the backing array so that it has exactly size() elements. /** Trims the backing array so that it has exactly {@link #size()} elements. */
	public void trim() {
		array = IntArrays.trim(array, size);
	}
	@Override
	public LongComparator comparator() {
		return c;
	}
	@Override
	public String toString() {
		StringBuffer s = new StringBuffer();
		s.append("[");
		for (int i = 0; i < size; i++) {
			if (i != 0)
				s.append(", ");
			s.append(refArray[array[i]]);
		}
		s.append("]");
		return s.toString();
	}
}