In a doubly linked list, which condition indicates that the list is empty?head is NULLhead->next is NULLhead->prev is NULLhead->next and head->prev are NULL

Breakdown of the Problem

1. We need to identify which condition indicates that a doubly linked list is empty.
2. The candidates for the condition include:
   • head is NULL
   • head->next is NULL
   • head->prev is NULL
   • head->next and head->prev are NULL

Relevant Concepts

• A doubly linked list consists of nodes that have two pointers: one pointing to the next node and one pointing to the previous node.
• Typically, an empty list is represented by the head pointer being NULL.

Analysis and Detail

1. head is NULL: This condition means that there are no nodes in the list, which is a clear indication that the list is empty.
2. head->next is NULL: This condition implies that there is at least one node (the head itself) in the list, but it has no subsequent nodes. Hence, the list is not empty.
3. head->prev is NULL: In a doubly linked list, the previous pointer of the head node being NULL is normal because there is no node before the head. This does not indicate that the list is empty.
4. head->next and head->prev are NULL: This condition would only apply if there exists a single node (the head) in the list, making the list not empty.

Verify and Summarize

Considering the above definitions and analyses, the only conclusive condition that indicates the doubly linked list is empty is when head is NULL.

Final Answer

The condition that indicates the list is empty is: head is NULL.