it.unimi.dsi.fastutil.ints.IntArrayPriorityQueue Maven / Gradle / Ivy
Show all versions of fastutil Show documentation
/*
* 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.ints;
import java.util.NoSuchElementException;
/**
* A type-specific array-based priority queue.
*
*
* Instances of this class represent a priority queue using a backing array—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.
*/
public class IntArrayPriorityQueue implements IntPriorityQueue, java.io.Serializable {
private static final long serialVersionUID = 1L;
/** The backing array. */
protected transient int array[] = IntArrays.EMPTY_ARRAY;
/** The number of elements in this queue. */
protected int size;
/** The type-specific comparator used in this queue. */
protected IntComparator c;
/** The first index, cached, if {@link #firstIndexValid} is true. */
protected transient int firstIndex;
/** Whether {@link #firstIndex} contains a valid value. */
protected transient boolean firstIndexValid;
/**
* Creates a new empty queue with a given capacity and comparator.
*
* @param capacity the initial capacity of this queue.
* @param c the comparator used in this queue, or {@code null} for the natural order.
*/
public IntArrayPriorityQueue(int capacity, IntComparator c) {
if (capacity > 0) this.array = new int[capacity];
this.c = c;
}
/**
* Creates a new empty queue with a given capacity and using the natural order.
*
* @param capacity the initial capacity of this queue.
*/
public IntArrayPriorityQueue(int capacity) {
this(capacity, null);
}
/**
* Creates a new empty queue with a given comparator.
*
* @param c the comparator used in this queue, or {@code null} for the natural order.
*/
public IntArrayPriorityQueue(IntComparator c) {
this(0, c);
}
/**
* Creates a new empty queue using the natural order.
*/
public IntArrayPriorityQueue() {
this(0, 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 a an array.
* @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 IntArrayPriorityQueue(final int[] a, int size, final IntComparator c) {
this(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 a an array.
* @param c the comparator used in this queue, or {@code null} for the natural order.
*/
public IntArrayPriorityQueue(final int[] a, final IntComparator c) {
this(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 a an array.
* @param size the number of elements to be included in the queue.
*/
public IntArrayPriorityQueue(final int[] a, int size) {
this(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 a an array.
*/
public IntArrayPriorityQueue(final int[] a) {
this(a, a.length);
}
/** Returns the index of the smallest element. */
private int findFirst() {
if (firstIndexValid) return this.firstIndex;
firstIndexValid = true;
int i = size;
int firstIndex = --i;
int first = array[firstIndex];
if (c == null) {
while (i-- != 0) if (((array[i]) < (first))) first = array[firstIndex = i];
} else while (i-- != 0) {
if (c.compare(array[i], first) < 0) first = array[firstIndex = i];
}
return this.firstIndex = firstIndex;
}
private void ensureNonEmpty() {
if (size == 0) throw new NoSuchElementException();
}
@Override
public void enqueue(int x) {
if (size == array.length) array = IntArrays.grow(array, size + 1);
if (firstIndexValid) {
if (c == null) {
if (((x) < (array[firstIndex]))) firstIndex = size;
} else if (c.compare(x, array[firstIndex]) < 0) firstIndex = size;
} else firstIndexValid = false;
array[size++] = x;
}
@Override
public int dequeueInt() {
ensureNonEmpty();
final int first = findFirst();
final int result = array[first];
System.arraycopy(array, first + 1, array, first, --size - first);
firstIndexValid = false;
return result;
}
@Override
public int firstInt() {
ensureNonEmpty();
return array[findFirst()];
}
@Override
public void changed() {
ensureNonEmpty();
firstIndexValid = false;
}
@Override
public int size() {
return size;
}
@Override
public void clear() {
size = 0;
firstIndexValid = false;
}
/** Trims the underlying array so that it has exactly {@link #size()} elements. */
public void trim() {
array = IntArrays.trim(array, size);
}
@Override
public IntComparator comparator() {
return c;
}
private void writeObject(java.io.ObjectOutputStream s) throws java.io.IOException {
s.defaultWriteObject();
s.writeInt(array.length);
for (int i = 0; i < size; i++) s.writeInt(array[i]);
}
private void readObject(java.io.ObjectInputStream s) throws java.io.IOException, ClassNotFoundException {
s.defaultReadObject();
array = new int[s.readInt()];
for (int i = 0; i < size; i++) array[i] = s.readInt();
}
}