Mega Code Archive
Sorts parts of the given array with the quicksort algorithm using the given comparator
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/**
* created Dec 12, 2007
*
* @by Marc Woerlein (woerlein@informatik.uni-erlangen.de)
*
* Copyright 2007 Marc Woerlein
*
* This file is part of parsemis.
*
* Licence:
* LGPL: http://www.gnu.org/licenses/lgpl.html
* EPL: http://www.eclipse.org/org/documents/epl-v10.php
* See the LICENSE file in the project's top-level directory for details.
*/
//package de.parsemis.utils;
/**
* generate ordered permutations of an integer array
*
* @author Marc Woerlein (woerlein@informatik.uni-erlangen.de)
*/
public class Permutations { /**
* Sorts parts of the given array with the quicksort algorithm using the
* given comparator.
*
* @param field
* the field to be sorted
* @param left
* the left start index in the field (inclusive)
* @param right
* the right end index in the field (inclusive)
* @param comp
* a comparator
*/
public static void quickSort(final int[] field, final int left,
final int right, final IntComparator comp) {
if (right - left == 2) {
if (comp.compare(field[left], field[left + 1]) > 0) {
swap(field, left, left + 1);
}
if (comp.compare(field[left + 1], field[right]) > 0) {
swap(field, right, left + 1);
}
if (comp.compare(field[left], field[left + 1]) > 0) {
swap(field, left, left + 1);
}
} else if (right - left == 1) {
if (comp.compare(field[left], field[right]) > 0) {
swap(field, left, right);
}
} else {
int l = left, r = right;
int pivot = (right - left) / 2 + left;
while (l < r) {
while ((pivot < r)
&& (comp.compare(field[pivot], field[r]) <= 0)) {
r--;
}
if (pivot < r) {
swap(field, pivot, r);
pivot = r;
}
while ((l < pivot)
&& (comp.compare(field[l], field[pivot]) <= 0)) {
l++;
}
if (l < pivot) {
swap(field, pivot, l);
pivot = l;
}
}
if (l - 1 - left > 0) {
quickSort(field, left, l - 1, comp);
}
if (right - (r + 1) > 0) {
quickSort(field, r + 1, right, comp);
}
}
}
/**
* Sorts the given <code>int[]</code> -field with quicksort using the
* given comparator.
*
* @param field
* the field to be sorted
* @param comp
* a comparator
* @return the sorted field (the same as <code>field</code>)
*/
public static int[] quickSort(final int[] field, final IntComparator comp) {
quickSort(field, 0, field.length - 1, comp);
return field;
}
/**
* swaps the values of the array at position i and j
*
* @param array
* @param i
* @param j
*/
public static void swap(final int array[], final int i, final int j) {
final int temp = array[i];
array[i] = array[j];
array[j] = temp;
}
}
interface IntComparator {
int compare(int a, int b);
}
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