it.unimi.dsi.fastutil.bytes.ByteHeapSemiIndirectPriorityQueue Maven / Gradle / Ivy
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/*
* Copyright (C) 2003-2024 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.bytes;
import java.util.NoSuchElementException;
import it.unimi.dsi.fastutil.ints.IntArrays;
/** A type-specific heap-based semi-indirect priority queue.
*
* Instances of this class use as reference list a reference array,
* which must be provided to each constructor. 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 allows one to enqueue several time the same index, but
* you must be careful when calling {@link #changed()}.
*/
public class ByteHeapSemiIndirectPriorityQueue implements ByteIndirectPriorityQueue {
/** The reference array. */
protected final byte refArray[];
/** The semi-indirect heap. */
protected int heap[] = IntArrays.EMPTY_ARRAY;
/** The number of elements in this queue. */
protected int size;
/** The type-specific comparator used in this queue. */
protected ByteComparator c;
/** 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 ByteHeapSemiIndirectPriorityQueue(byte[] refArray, int capacity, ByteComparator c) {
if (capacity > 0) this.heap = 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 ByteHeapSemiIndirectPriorityQueue(byte[] 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 ByteHeapSemiIndirectPriorityQueue(byte[] refArray, ByteComparator 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 ByteHeapSemiIndirectPriorityQueue(final byte[] 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 ByteHeapSemiIndirectPriorityQueue(final byte[] refArray, final int[] a, int size, final ByteComparator c) {
this(refArray, 0, c);
this.heap = a;
this.size = size;
ByteSemiIndirectHeaps.makeHeap(refArray, a, 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 ByteHeapSemiIndirectPriorityQueue(final byte[] refArray, final int[] a, final ByteComparator 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 ByteHeapSemiIndirectPriorityQueue(final byte[] 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 ByteHeapSemiIndirectPriorityQueue(final byte[] refArray, final int[] a) {
this(refArray, a, a.length);
}
/** Ensures that the given index is a valid 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 + ")");
}
@Override
public void enqueue(int x) {
ensureElement(x);
if (size == heap.length) heap = IntArrays.grow(heap, size + 1);
heap[size++] = x;
ByteSemiIndirectHeaps.upHeap(refArray, heap, size, size - 1, c);
}
@Override
public int dequeue() {
if (size == 0) throw new NoSuchElementException();
final int result = heap[0];
heap[0] = heap[--size];
if (size != 0) ByteSemiIndirectHeaps.downHeap(refArray, heap, size, 0, c);
return result;
}
@Override
public int first() {
if (size == 0) throw new NoSuchElementException();
return heap[0];
}
/** {@inheritDoc}
*
*
The caller must guarantee that when this method is called the
* index of the first element appears just once in the queue. Failure to do so
* will bring the queue in an inconsistent state, and will cause
* unpredictable behaviour.
*/
@Override
public void changed() {
ByteSemiIndirectHeaps.downHeap(refArray, heap, size, 0, c);
}
/** Rebuilds this heap in a bottom-up fashion (in linear time). */
@Override
public void allChanged() { ByteSemiIndirectHeaps.makeHeap(refArray, heap, size, c); }
@Override
public int size() { return size; }
@Override
public void clear() { size = 0; }
/** Trims the backing array so that it has exactly {@link #size()} elements. */
public void trim() {
heap = IntArrays.trim(heap, size);
}
@Override
public ByteComparator comparator() { return c; }
/** 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(final int[] a) { return c == null ? ByteSemiIndirectHeaps.front(refArray, heap, size, a) : ByteSemiIndirectHeaps.front(refArray, heap, size, a, 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[heap [i]]);
}
s.append("]");
return s.toString();
}
}