it.unimi.dsi.fastutil.floats.FloatHeapSemiIndirectPriorityQueue 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.floats;
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 FloatHeapSemiIndirectPriorityQueue implements FloatIndirectPriorityQueue {
/** The reference array. */
protected final float 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 FloatComparator 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 FloatHeapSemiIndirectPriorityQueue(float[] refArray, int capacity, FloatComparator 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 FloatHeapSemiIndirectPriorityQueue(float[] 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 FloatHeapSemiIndirectPriorityQueue(float[] refArray, FloatComparator 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 FloatHeapSemiIndirectPriorityQueue(final float[] 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 FloatHeapSemiIndirectPriorityQueue(final float[] refArray, final int[] a, int size, final FloatComparator c) {
this(refArray, 0, c);
this.heap = a;
this.size = size;
FloatSemiIndirectHeaps.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 FloatHeapSemiIndirectPriorityQueue(final float[] refArray, final int[] a, final FloatComparator 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 FloatHeapSemiIndirectPriorityQueue(final float[] 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 FloatHeapSemiIndirectPriorityQueue(final float[] 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;
FloatSemiIndirectHeaps.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) FloatSemiIndirectHeaps.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() {
FloatSemiIndirectHeaps.downHeap(refArray, heap, size, 0, c);
}
/** Rebuilds this heap in a bottom-up fashion (in linear time). */
@Override
public void allChanged() {
FloatSemiIndirectHeaps.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 FloatComparator 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 ? FloatSemiIndirectHeaps.front(refArray, heap, size, a) : FloatSemiIndirectHeaps.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();
}
}