Quicksort.java

public class Quicksort
{
    public static void main(String[] args) {
        int a[] = new int[] {
            10, 4, 4, 8, 0, 8, 9, 7, 3, 7, 6
        };

        Quicksort.sort(a);

        for (int e: a) {
            System.out.print(e);
            System.out.print(" ");
        };
        
        System.out.println();
    }

    public static void sort(int[] a)
    {
        qsort(a, 0, a.length - 1);
    }
 
    private static void qsort(int[] a, int start, int stop)
    {
        if (start < stop) {
            int pivot = pos(a, start, stop);
            qsort(a, start, pivot);
            qsort(a, pivot + 1, stop);
        }
    }
 
    private static int pos(int[] a, int start, int stop)
    {
        int i = start;
        int j = stop;
        int pivot = i;
 
        while (i < j)
        {
            if (a[i] > a[j])
            {
                int aux = a[i];
                a[i] = a[j];
                a[j] = aux;
                pivot = pivot == i ? j : i;
            }
            if (pivot == i)
            {
                j--;
            }
            else
            {
                i++;
            }
        }
        return pivot;
    }
}