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* Copyright (C) 2003-2016 Paolo Boldi and Sebastiano Vigna
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package it.unimi.dsi.fastutil.floats;
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 heap[inv[i]]==i when
* inv[i]>=0, and inv[heap[i]]==i for all elements
* in the heap.
*/
public class FloatIndirectHeaps {
private FloatIndirectHeaps() {
}
/**
* 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 null for the
* natural order.
* @return the new position in the heap of the element of heap index
* i.
*/
public static int downHeap(final float[] refArray, final int[] heap, final int[] inv, final int size, int i, final FloatComparator c) {
assert i < size;
final int e = heap[i];
final float 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 && (Float.compare((refArray[heap[right]]), (refArray[t])) < 0)) t = heap[child = right];
if ((Float.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 null for the
* natural order.
* @return the new position in the heap of the element of heap index
* i.
*/
public static int upHeap(final float[] refArray, final int[] heap, final int[] inv, final int size, int i, final FloatComparator c) {
assert i < size;
final int e = heap[i];
final float E = refArray[e];
if (c == null) while (i != 0) {
final int parent = (i - 1) >>> 1;
final int t = heap[parent];
if ((Float.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 null for the
* natural order.
*/
public static void makeHeap(final float[] refArray, final int offset, final int length, final int[] heap, final int[] inv, final FloatComparator c) {
FloatArrays.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 refArray.
* @param inv
* the inversion array.
* @param size
* the number of elements in the heap.
* @param c
* a type-specific comparator, or null for the
* natural order.
*/
public static void makeHeap(final float[] refArray, final int[] heap, final int[] inv, final int size, final FloatComparator c) {
int i = size >>> 1;
while (i-- != 0)
downHeap(refArray, heap, inv, size, i, c);
}
}