it.unimi.dsi.fastutil.shorts.ShortHeapIndirectPriorityQueue Maven / Gradle / Ivy
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/*
* Copyright (C) 2003-2023 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.Arrays;
import java.util.NoSuchElementException;
/**
* A type-specific heap-based indirect priority queue.
*
*
* Instances of this class use an additional inversion array, of the same length of the
* reference array, to keep track of the heap position containing a given element of the reference
* array. The priority queue is represented using a heap. The heap is enlarged as needed, but it is
* never shrunk. Use the {@link #trim()} method to reduce its size, if necessary.
*
* @implSpec This implementation does not allow one to enqueue several times the same
* index.
*/
public class ShortHeapIndirectPriorityQueue extends ShortHeapSemiIndirectPriorityQueue {
/** The inversion array. */
protected final int inv[];
/**
* Creates a new empty queue 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 ShortHeapIndirectPriorityQueue(short[] refArray, int capacity, ShortComparator c) {
super(refArray, capacity, c);
this.inv = new int[refArray.length];
Arrays.fill(inv, -1);
}
/**
* Creates a new empty queue with a given capacity and using the natural order.
*
* @param refArray the reference array.
* @param capacity the initial capacity of this queue.
*/
public ShortHeapIndirectPriorityQueue(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 ShortHeapIndirectPriorityQueue(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 ShortHeapIndirectPriorityQueue(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. The first {@code size}
* element of the array will be rearranged so to form a heap (this is more efficient than enqueing
* the elements of {@code a} one by one).
*
* @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 ShortHeapIndirectPriorityQueue(final short[] refArray, final int[] a, final int size, final ShortComparator c) {
this(refArray, 0, c);
this.heap = a;
this.size = size;
int i = size;
while (i-- != 0) {
if (inv[a[i]] != -1) throw new IllegalArgumentException("Index " + a[i] + " appears twice in the heap");
inv[a[i]] = i;
}
ShortIndirectHeaps.makeHeap(refArray, a, inv, size, c);
}
/**
* Wraps a given array in a queue using a given comparator.
*
*
* The queue returned by this method will be backed by the given array. The elements of the array
* will be rearranged so to form a heap (this is more efficient than enqueing the elements of
* {@code a} one by one).
*
* @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 ShortHeapIndirectPriorityQueue(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. The first {@code size}
* element of the array will be rearranged so to form a heap (this is more efficient than enqueing
* the elements of {@code a} one by one).
*
* @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 ShortHeapIndirectPriorityQueue(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. The elements of the array
* will be rearranged so to form a heap (this is more efficient than enqueing the elements of
* {@code a} one by one).
*
* @param refArray the reference array.
* @param a an array of indices into {@code refArray}.
*/
public ShortHeapIndirectPriorityQueue(final short[] refArray, final int[] a) {
this(refArray, a, a.length);
}
@Override
public void enqueue(final int x) {
if (inv[x] >= 0) throw new IllegalArgumentException("Index " + x + " belongs to the queue");
if (size == heap.length) heap = IntArrays.grow(heap, size + 1);
inv[heap[size] = x] = size++;
ShortIndirectHeaps.upHeap(refArray, heap, inv, size, size - 1, c);
}
@Override
public boolean contains(final int index) {
return inv[index] >= 0;
}
@Override
public int dequeue() {
if (size == 0) throw new NoSuchElementException();
final int result = heap[0];
if (--size != 0) inv[heap[0] = heap[size]] = 0;
inv[result] = -1;
if (size != 0) ShortIndirectHeaps.downHeap(refArray, heap, inv, size, 0, c);
return result;
}
@Override
public void changed() {
ShortIndirectHeaps.downHeap(refArray, heap, inv, size, 0, c);
}
@Override
public void changed(final int index) {
final int pos = inv[index];
if (pos < 0) throw new IllegalArgumentException("Index " + index + " does not belong to the queue");
final int newPos = ShortIndirectHeaps.upHeap(refArray, heap, inv, size, pos, c);
ShortIndirectHeaps.downHeap(refArray, heap, inv, size, newPos, c);
}
/** Rebuilds this queue in a bottom-up fashion (in linear time). */
@Override
public void allChanged() {
ShortIndirectHeaps.makeHeap(refArray, heap, inv, size, c);
}
@Override
public boolean remove(final int index) {
final int result = inv[index];
if (result < 0) return false;
inv[index] = -1;
if (result < --size) {
inv[heap[result] = heap[size]] = result;
final int newPos = ShortIndirectHeaps.upHeap(refArray, heap, inv, size, result, c);
ShortIndirectHeaps.downHeap(refArray, heap, inv, size, newPos, c);
}
return true;
}
@Override
public void clear() {
size = 0;
Arrays.fill(inv, -1);
}
}