it.unimi.dsi.fastutil.doubles.DoubleIndirectHeaps 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;
import java.util.Arrays;
/**
* A class providing static methods and objects that do useful things with indirect heaps.
*
*
* An indirect heap is an extension of a semi-indirect heap using also an inversion array
* of the same length as the reference array, satisfying the relation {@code heap[inv[i]]==i} when
* {@code inv[i]>=0}, and {@code inv[heap[i]]==i} for all elements in the heap.
*/
public final class DoubleIndirectHeaps {
private DoubleIndirectHeaps() {
}
/**
* Moves the given element down into the indirect heap until it reaches the lowest possible
* position.
*
* @param refArray the reference array.
* @param heap the indirect heap (starting at 0).
* @param inv the inversion array.
* @param size the number of elements in the heap.
* @param i the index in the heap of the element to be moved down.
* @param c a type-specific comparator, or {@code null} for the natural order.
* @return the new position in the heap of the element of heap index {@code i}.
*/
public static int downHeap(final double[] refArray, final int[] heap, final int[] inv, final int size, int i, final DoubleComparator c) {
assert i < size;
final int e = heap[i];
final double E = refArray[e];
int child;
if (c == null) while ((child = (i << 1) + 1) < size) {
int t = heap[child];
final int right = child + 1;
if (right < size && (Double.compare((refArray[heap[right]]), (refArray[t])) < 0)) t = heap[child = right];
if ((Double.compare((E), (refArray[t])) <= 0)) break;
heap[i] = t;
inv[heap[i]] = i;
i = child;
}
else while ((child = (i << 1) + 1) < size) {
int t = heap[child];
final int right = child + 1;
if (right < size && c.compare(refArray[heap[right]], refArray[t]) < 0) t = heap[child = right];
if (c.compare(E, refArray[t]) <= 0) break;
heap[i] = t;
inv[heap[i]] = i;
i = child;
}
heap[i] = e;
inv[e] = i;
return i;
}
/**
* Moves the given element up in the indirect heap until it reaches the highest possible position.
*
* Note that in principle after this call the heap property may be violated.
*
* @param refArray the reference array.
* @param heap the indirect heap (starting at 0).
* @param inv the inversion array.
* @param size the number of elements in the heap.
* @param i the index in the heap of the element to be moved up.
* @param c a type-specific comparator, or {@code null} for the natural order.
* @return the new position in the heap of the element of heap index {@code i}.
*/
public static int upHeap(final double[] refArray, final int[] heap, final int[] inv, final int size, int i, final DoubleComparator c) {
assert i < size;
final int e = heap[i];
final double E = refArray[e];
if (c == null) while (i != 0) {
final int parent = (i - 1) >>> 1;
final int t = heap[parent];
if ((Double.compare((refArray[t]), (E)) <= 0)) break;
heap[i] = t;
inv[heap[i]] = i;
i = parent;
}
else while (i != 0) {
final int parent = (i - 1) >>> 1;
final int t = heap[parent];
if (c.compare(refArray[t], E) <= 0) break;
heap[i] = t;
inv[heap[i]] = i;
i = parent;
}
heap[i] = e;
inv[e] = i;
return i;
}
/**
* Creates an indirect heap in the given array.
*
* @param refArray the reference array.
* @param offset the first element of the reference array to be put in the heap.
* @param length the number of elements to be put in the heap.
* @param heap the array where the heap is to be created.
* @param inv the inversion array.
* @param c a type-specific comparator, or {@code null} for the natural order.
*/
public static void makeHeap(final double[] refArray, final int offset, final int length, final int[] heap, final int[] inv, final DoubleComparator c) {
DoubleArrays.ensureOffsetLength(refArray, offset, length);
if (heap.length < length) throw new IllegalArgumentException("The heap length (" + heap.length + ") is smaller than the number of elements (" + length + ")");
if (inv.length < refArray.length) throw new IllegalArgumentException("The inversion array length (" + heap.length + ") is smaller than the length of the reference array (" + refArray.length + ")");
Arrays.fill(inv, 0, refArray.length, -1);
int i = length;
while (i-- != 0) inv[heap[i] = offset + i] = i;
i = length >>> 1;
while (i-- != 0) downHeap(refArray, heap, inv, length, i, c);
}
/**
* Creates an indirect heap from a given index array.
*
* @param refArray the reference array.
* @param heap an array containing indices into {@code refArray}.
* @param inv the inversion array.
* @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[] refArray, final int[] heap, final int[] inv, final int size, final DoubleComparator c) {
int i = size >>> 1;
while (i-- != 0) downHeap(refArray, heap, inv, size, i, c);
}
}