Why do doubly linked lists enable faster deletions compared to singly linked lists?

• A. Because the list is shorter
• B. Because each node has a prev pointer, enabling immediate unlinking
• C. Because they store values in arrays
• D. Because they do not require a dummy head

Answer: (B)

The key idea is that a doubly linked list stores a link to the previous node in addition to the next one. When you delete a node, you can immediately unlink it by updating the neighboring pointers: set the previous node’s next to the node’s next, and set the next node’s prev to the node’s prev. This can be done in constant time if you have a reference to the node being deleted, because no traversal is needed. In a singly linked list you only have a next pointer, so to delete a node you typically must find its predecessor by walking from the head, which takes linear time in the worst case. The extra prev pointer in each node thus enables immediate unlinking and faster deletions. The other options don’t explain this mechanism: list length, storing values in arrays, or dummy heads don’t inherently remove the need to locate or adjust the predecessor.