/*
 * Copyright (C) 2003-2017 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);
	}
}
