When reversing a singly linked list recursively, what is a typical base case?

• A. Head is NULL or head.next is NULL.
• B. Head is the tail.
• C. Head is the middle node.
• D. List has more than one node.

Answer: (A)

In recursive reversal, you stop when the part of the list you’re about to reverse is empty or just one node. That means the base case is when head is null or head.next is null. This works because a zero-node or a single-node list is already reversed, so you can return that node as the new head and let the recursion unwind.

During the recursive step, you reverse the rest of the list starting from head.next, then flip the current link by making head.next.next point back to head, and set head.next to null to mark the new end. This base case naturally handles both an empty list and a single-node list, which is why it’s the typical termination condition.

The other notions aren’t proper termination conditions for all lists: using “head is the tail” is not a general check you can rely on in code, since the tail concept is only known at runtime and the real stop condition is the end of the list (head.next being null). A middle node or a condition like “more than one node” doesn’t indicate a safe stop point for the recursive reversal.