Loop in linked list

Question

Consider the following code fragment to detect a cycle/loop in a given singly linked list. Find the missing statement S1.

1.   p!=NULL
2.   q!=NULL
3.   (p!=NULL || q!=NULL)
4.   (p!=NULL && q!==NULL)

Comments

https://gateoverflow.in/99515/data-structure

Answer 1

I think ans is OPTION 3 because suppose when p==null that condition also need to be checked and q=null because we want to end while loop as soon as fast pointer which is 'q' either loops or reaches end.