public class QuickSort { public static abstract class Comparator { public abstract int compare(Object obj1, Object obj2); } private Comparator mComparator; public QuickSort(Comparator comparator) { mComparator = comparator; } /** This is a generic version of C.A.R Hoare's Quick Sort * algorithm. This will handle arrays that are already * sorted, and arrays with duplicate keys.
* * If you think of a one dimensional array as going from * the lowest index on the left to the highest index on the right * then the parameters to this function are lowest index or * left and highest index or right. The first time you call * this function it will be with the parameters 0, a.length - 1. * * @param a an Object array * @param lo0 left boundary of array partition * @param hi0 right boundary of array partition */ private void qsort(Object[] a, int lo0, int hi0) { int lo = lo0; int hi = hi0; if ( hi0 > lo0) { /* Arbitrarily establishing partition element as the midpoint of * the array. */ Object mid = a[ ( lo0 + hi0 ) / 2 ]; // loop through the array until indices cross while ( lo <= hi ) { /* find the first element that is greater than or equal to * the partition element starting from the left Index. */ while (( lo < hi0 ) && ( mComparator.compare(a[lo], mid) < 0 )) ++lo; /* find an element that is smaller than or equal to * the partition element starting from the right Index. */ while (( hi > lo0 ) && ( mComparator.compare(a[hi], mid) > 0 )) --hi; // if the indexes have not crossed, swap if ( lo <= hi ) { swap(a, lo, hi); ++lo; --hi; } } /* If the right index has not reached the left side of array * must now sort the left partition. */ if ( lo0 < hi ) qsort( a, lo0, hi ); /* If the left index has not reached the right side of array * must now sort the right partition. */ if ( lo < hi0 ) qsort( a, lo, hi0 ); } } private static void swap(Object[] a, int i, int j) { Object temp = a[i]; a[i] = a[j]; a[j] = temp; } public void sort(Object[] a) { qsort(a, 0, a.length - 1); } public void sort(Object[] a, int length) { qsort(a, 0, length - 1); } }