Quick Sort

gistfile1.java

public static void quickSort(int[] a, int p, int r)
    {
        if(p<r)
        {
            int q=partition(a,p,r);
            quickSort(a,p,q);
            quickSort(a,q+1,r);
        }
    }

    private static int partition(int[] a, int p, int r) {

        int x = a[p];
        int i = p-1 ;
        int j = r+1 ;

        while (true) {
            i++;
            while ( i< r && a[i] < x)
                i++;
            j--;
            while (j>p && a[j] > x)
                j--;

            if (i < j)
                swap(a, i, j);
            else
                return j;
        }
    }