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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 PACKAGE;
#if KEY_CLASS_Object
import java.util.Comparator;
#endif
/** A class providing static methods and objects that do useful things with heaps.
*
* <p>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 HEAPS {
private HEAPS() {}
/** 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}.
*/
SUPPRESS_WARNINGS_KEY_UNCHECKED
public static KEY_GENERIC int downHeap(final KEY_GENERIC_TYPE[] heap, final int size, int i, final KEY_COMPARATOR KEY_SUPER_GENERIC c) {
assert i < size;
final KEY_GENERIC_TYPE e = heap[i];
int child;
if (c == null)
while ((child = (i << 1) + 1) < size) {
KEY_GENERIC_TYPE t = heap[child];
final int right = child + 1;
if (right < size && KEY_LESS(heap[right], t)) t = heap[child = right];
if (KEY_LESSEQ(e, t)) break;
heap[i] = t;
i = child;
}
else
while ((child = (i << 1) + 1) < size) {
KEY_GENERIC_TYPE 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}.
*/
SUPPRESS_WARNINGS_KEY_UNCHECKED
public static KEY_GENERIC int upHeap(final KEY_GENERIC_TYPE[] heap, final int size, int i, final KEY_COMPARATOR KEY_GENERIC c) {
assert i < size;
final KEY_GENERIC_TYPE e = heap[i];
if (c == null)
while (i != 0) {
final int parent = (i - 1) >>> 1;
final KEY_GENERIC_TYPE t = heap[parent];
if (KEY_LESSEQ(t, e)) break;
heap[i] = t;
i = parent;
}
else
while (i != 0) {
final int parent = (i - 1) >>> 1;
final KEY_GENERIC_TYPE 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 KEY_GENERIC void makeHeap(final KEY_GENERIC_TYPE[] heap, final int size, final KEY_COMPARATOR KEY_GENERIC c) {
int i = size >>> 1;
while(i-- != 0) downHeap(heap, size, i, c);
}
}
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