org.openimaj.math.util.ParallelQuicksortDescending Maven / Gradle / Ivy
/**
* Copyright (c) 2011, The University of Southampton and the individual contributors.
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without modification,
* are permitted provided that the following conditions are met:
*
* * Redistributions of source code must retain the above copyright notice,
* this list of conditions and the following disclaimer.
*
* * Redistributions in binary form must reproduce the above copyright notice,
* this list of conditions and the following disclaimer in the documentation
* and/or other materials provided with the distribution.
*
* * Neither the name of the University of Southampton nor the names of its
* contributors may be used to endorse or promote products derived from this
* software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
* WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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package org.openimaj.math.util;
/**
* Sort parallel arrays. Arrays are sorted in-place. The first array determines
* the order, and is sorted into descending order.
*
*
* @author Jonathan Hare
* @author Sina Samangooei
*/
public final class ParallelQuicksortDescending {
/**
* Sort parallel arrays. Arrays are sorted in-place. The first array
* determines the order, and is sorted into descending order.
*
* Implementation inspired by this stackoverflow page: http://stackoverflow.com/questions/951848/java-array-sort-quick-way-to-
* get-a-sorted-list-of-indices-of-an-array
*
* @param main
* the values to use for determining the order
* @param indices
* the second array
*/
public static void sort(double[] main, int[] indices) {
sort(main, indices, 0, indices.length - 1);
}
/**
* Sort parallel arrays. Arrays are sorted in-place. The first array
* determines the order, and is sorted into descending order.
*
* Implementation inspired by this stackoverflow page: http://stackoverflow.com/questions/951848/java-array-sort-quick-way-to-
* get-a-sorted-list-of-indices-of-an-array
*
* @param main
* the values to use for determining the order
* @param indices
* the second array
* @param left
* the starting index
* @param right
* the ending index
*/
public static void sort(double[] main, int[] indices, int left,
int right)
{
if (right <= left) {
return;
}
int i = partitionDesc(main, indices, left, right);
sort(main, indices, left, i - 1);
sort(main, indices, i + 1, right);
}
// partition a[left] to a[right], assumes left < right
private static int partitionDesc(double[] a, int[] index, int left, int right) {
int i = left - 1;
int j = right;
while (true) {
while (a[++i] > a[right])
// find item on left to swap
; // a[right] acts as sentinel
while (a[right] > a[--j])
// find item on right to swap
if (j == left) {
break; // don't go out-of-bounds
}
if (i >= j) {
break; // check if pointers cross
}
exch(a, index, i, j); // swap two elements into place
}
exch(a, index, i, right); // swap with partition element
return i;
}
// exchange a[i] and a[j]
private static void exch(double[] a, int[] index, int i, int j) {
double swap = a[i];
a[i] = a[j];
a[j] = swap;
int b = index[i];
index[i] = index[j];
index[j] = b;
}
private ParallelQuicksortDescending() {
}
}