快速排序

public static void quickSort(int[] a, int l, int r){
        if (l < r){
            int i,j,x;
            i = l;
            j = r;
            x = a[i];
            while (i < j){
                while(i < j && a[j] > x){
                    j--;
                }

                if (i<j){
                    a[i++] = a[j];
                }

                while (i < j && a[i] <x){
                    i ++;
                }

                if (i < j){
                    a[j--] = a[i];
                }

            } //end while
            a[i] = x;
            quickSort(a, l, i-1);
            quickSort(a, i+1, r);
        } //end if
    }