/*		 
 * Copyright (C) 2003-2014 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 #keyclass(Object)
import java.util.Comparator;
#endif

import java.util.Arrays;

/** A class providing static methods and objects that do useful things with indirect heaps.
 *
 * <P>An indirect heap is an extension of a semi-indirect heap using also an
 * <em>inversion array</em> of the same length as the reference array,
 * satisfying the relation <code>heap[inv[i]]==i</code> when
 * <code>inv[i]&gt;=0</code>, and <code>inv[heap[i]]==i</code> for all elements in the heap.
 */

public class INDIRECT_HEAPS {

	private INDIRECT_HEAPS() {}

	/** 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</code> for the natural order.
	 * @return the new position in the heap of the element of heap index <code>i</code>.
	 */

	SUPPRESS_WARNINGS_KEY_UNCHECKED
	public static KEY_GENERIC int downHeap( final KEY_GENERIC_TYPE[] refArray, final int[] heap, final int[] inv, final int size, int i, final KEY_COMPARATOR KEY_GENERIC c ) {
		if ( i >= size ) throw new IllegalArgumentException( "Heap position (" + i + ") is larger than or equal to heap size (" + size + ")" );

		final int e = heap[ i ];
		final KEY_GENERIC_TYPE E = refArray[ e ];
		int child;

		if ( c == null )
			while ( ( child = 2 * i + 1 ) < size ) {
				if ( child + 1 < size && KEY_LESS( refArray[ heap[ child + 1 ] ], refArray[ heap[ child ] ] ) ) child++;
				if ( KEY_LESSEQ( E, refArray[ heap[ child ] ] ) ) break;
				heap[ i ] = heap[ child ];
				inv[ heap[ i ] ] = i;
				i = child;
			}
		else 
			while ( ( child = 2 * i + 1 ) < size ) {
				if ( child + 1 < size && c.compare( refArray[ heap[ child + 1 ] ], refArray[ heap[ child ] ] ) < 0 ) child++;
				if ( c.compare( E, refArray[ heap[ child ] ] ) <= 0 ) break;
				heap[ i ] = heap[ child ];
				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</code> for the natural order.
	 * @return the new position in the heap of the element of heap index <code>i</code>.
	 */

	SUPPRESS_WARNINGS_KEY_UNCHECKED
	public static KEY_GENERIC int upHeap( final KEY_GENERIC_TYPE[] refArray, final int[] heap, final int[] inv, final int size, int i, final KEY_COMPARATOR KEY_GENERIC c ) {
		if ( i >= size ) throw new IllegalArgumentException( "Heap position (" + i + ") is larger than or equal to heap size (" + size + ")" );

		final int e = heap[ i ];
		final KEY_GENERIC_TYPE E = refArray[ e ];
		int parent;

		if ( c == null )
			while ( i != 0 && ( parent = ( i - 1 ) / 2 ) >= 0 ) {
				if ( KEY_LESSEQ( refArray[ heap[ parent ] ], E ) ) break;
				heap[ i ] = heap[ parent ];
				inv[ heap[ i ] ] = i;
				i = parent;
			}
		else
			while ( i != 0 && ( parent = ( i - 1 ) / 2 ) >= 0 ) {
				if ( c.compare( refArray[ heap[ parent ] ], E ) <= 0 ) break;
				heap[ i ] = heap[ parent ]; 
				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</code> for the natural order.
	 */

	public static KEY_GENERIC void makeHeap( final KEY_GENERIC_TYPE[] refArray, final int offset, final int length, final int[] heap, final int[] inv, final KEY_COMPARATOR KEY_GENERIC c ) {
		ARRAYS.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 / 2;
		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</code>.
	 * @param inv the inversion array.
	 * @param size the number of elements in the heap.
	 * @param c a type-specific comparator, or <code>null</code> for the natural order.
	 */

	public static KEY_GENERIC void makeHeap( final KEY_GENERIC_TYPE[] refArray, final int[] heap, final int[] inv, final int size, final KEY_COMPARATOR KEY_GENERIC c ) {
		int i = size / 2;
		while( i-- != 0 ) downHeap( refArray, heap, inv, size, i, c );
	}
}
