it.unimi.dsi.fastutil.doubles.DoubleHeaps 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.doubles;
/**
* A class providing static methods and objects that do useful things with heaps.
*
*
* The static methods of this class allow to treat arrays as 0-based heaps. They are used in the
* implementation of heap-based queues, but they may be also used directly.
*
*/
public final class DoubleHeaps {
private DoubleHeaps() {
}
/**
* Moves the given element down into the heap until it reaches the lowest possible position.
*
* @param heap the heap (starting at 0).
* @param size the number of elements in the heap.
* @param i the index of the element that must be moved down.
* @param c a type-specific comparator, or {@code null} for the natural order.
* @return the new position of the element of index {@code i}.
*/
public static int downHeap(final double[] heap, final int size, int i, final DoubleComparator c) {
assert i < size;
final double e = heap[i];
int child;
if (c == null) while ((child = (i << 1) + 1) < size) {
double t = heap[child];
final int right = child + 1;
if (right < size && (Double.compare((heap[right]), (t)) < 0)) t = heap[child = right];
if ((Double.compare((e), (t)) <= 0)) break;
heap[i] = t;
i = child;
}
else while ((child = (i << 1) + 1) < size) {
double t = heap[child];
final int right = child + 1;
if (right < size && c.compare(heap[right], t) < 0) t = heap[child = right];
if (c.compare(e, t) <= 0) break;
heap[i] = t;
i = child;
}
heap[i] = e;
return i;
}
/**
* Moves the given element up in the heap until it reaches the highest possible position.
*
* @param heap the heap (starting at 0).
* @param size the number of elements in the heap.
* @param i the index of the element that must be moved up.
* @param c a type-specific comparator, or {@code null} for the natural order.
* @return the new position of the element of index {@code i}.
*/
public static int upHeap(final double[] heap, final int size, int i, final DoubleComparator c) {
assert i < size;
final double e = heap[i];
if (c == null) while (i != 0) {
final int parent = (i - 1) >>> 1;
final double t = heap[parent];
if ((Double.compare((t), (e)) <= 0)) break;
heap[i] = t;
i = parent;
}
else while (i != 0) {
final int parent = (i - 1) >>> 1;
final double t = heap[parent];
if (c.compare(t, e) <= 0) break;
heap[i] = t;
i = parent;
}
heap[i] = e;
return i;
}
/**
* Makes an array into a heap.
*
* @param heap the heap (starting at 0).
* @param size the number of elements in the heap.
* @param c a type-specific comparator, or {@code null} for the natural order.
*/
public static void makeHeap(final double[] heap, final int size, final DoubleComparator c) {
int i = size >>> 1;
while (i-- != 0) downHeap(heap, size, i, c);
}
}