public static int rank(int[] array, int k, int front, int rear)

 {

     if(front > rear)

         return -1;

     int mid = front + (rear - front) / 2;

     if(k == array[mid])

         return mid;

     else if(k > array[mid])

         return rank(array, k, mid + 1, rear);

     else

         return rank(array, k, front, mid - 1);

 }