it.unimi.dsi.fastutil.shorts.ShortArrayIndirectPriorityQueue Maven / Gradle / Ivy
Show all versions of fastutil Show documentation
/*
* Copyright (C) 2003-2022 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.shorts;
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 {@link #trim()} method to reduce its size, if necessary.
*
* @implSpec 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 ShortArrayIndirectPriorityQueue implements ShortIndirectPriorityQueue {
/** The reference array. */
protected short refArray[];
/** The backing array. */
protected int array[] = IntArrays.EMPTY_ARRAY;
/** The number of elements in this queue. */
protected int size;
/** The type-specific comparator used in this queue. */
protected ShortComparator c;
/** The first index, cached, if {@link #firstIndexValid} is true. */
protected int firstIndex;
/** Whether {@link #firstIndex} contains a valid value. */
protected boolean firstIndexValid;
/**
* 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 ShortArrayIndirectPriorityQueue(short[] refArray, int capacity, ShortComparator 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.
*
* @param refArray the reference array.
* @param capacity the initial capacity of this queue.
*/
public ShortArrayIndirectPriorityQueue(short[] 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.
*
* @param refArray the reference array.
* @param c the comparator used in this queue, or {@code null} for the natural order.
*/
public ShortArrayIndirectPriorityQueue(short[] refArray, ShortComparator 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.
*
* @param refArray the reference array.
*/
public ShortArrayIndirectPriorityQueue(short[] 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.
*
* @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 ShortArrayIndirectPriorityQueue(final short[] refArray, final int[] a, int size, final ShortComparator 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.
*
* @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 ShortArrayIndirectPriorityQueue(final short[] refArray, final int[] a, final ShortComparator 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.
*
* @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 ShortArrayIndirectPriorityQueue(final short[] 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.
*
* @param refArray the reference array.
* @param a an array of indices into {@code refArray}.
*/
public ShortArrayIndirectPriorityQueue(final short[] refArray, final int[] a) {
this(refArray, a, a.length);
}
/** 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;
short 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 {@link #array}) of the largest element. */
private int findLast() {
int i = size;
int lastIndex = --i;
short 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.
*
* @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 {@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
* {@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. */
@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.
*
* @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 short 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 {@link #size()} elements. */
public void trim() {
array = IntArrays.trim(array, size);
}
@Override
public ShortComparator 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();
}
}