Find the kth smallest.. algo
element_type Ksmall(k, A, First, Last)
1. Choose a pivot element p from A[First…Last];
2. if (k < Pindex - F + 1) return Ksmall(k, A, First, Pindex-1);
3. else if (k == Pindex - First + 1) return p;
4. else return Ksmall(k - (Pindex - First + 1) , A, Pindex+1, L);