How does a doubly linked list differ from a singly linked list in terms of per-node pointers and memory usage?

• A. Doubly uses next and prev; higher per-node memory overhead but enables bidirectional traversal
• B. Doubly uses two next pointers
• C. Doubly uses only prev pointer
• D. Singly uses two prev pointers

Answer: (C)

In a doubly linked list, each node stores two pointers: one to the next node and one to the previous node. This is why per-node memory usage is higher than in a singly linked list, where each node keeps only a single next pointer. The payoff is bidirectional traversal: you can move forward using the next pointer and backward using the prev pointer without starting from the head each time. The extra pointer is the source of the increased memory overhead, but it enables convenient backwards navigation, easier deletions, and simpler insertions before a given node. The option that mentions two next pointers would not provide backward navigation on its own, the idea of using only a previous pointer would eliminate forward traversal, and a singly linked list uses one pointer, not two prev pointers.