What is a doubly linked list?

• A. A linked list where each node has two links: a next pointer and a prev pointer, allowing bidirectional traversal.
• B. A singly linked list with backward pointers.
• C. A binary tree with left and right links.
• D. An array-based list with a fixed capacity.

Answer: (A)

Key concept: a doubly linked list is a chain of nodes where each node stores two pointers: one to the next node and one to the previous node, allowing traversal in both directions. This bidirectional navigation makes it easy to move forward or backward through the list and to insert or remove nodes when you already have a reference to a node, since you can re-link neighbors by updating both pointers without starting from the head each time. Compared to a singly linked list, which has only a next pointer and supports forward movement, the extra previous pointer enables backward traversal. It’s not a binary tree, which uses left and right child links to form a branching structure, and it’s not an array-based list, which stores elements contiguously in memory and typically has fixed capacity. So the description of each node having two links, next and prev, and supporting bidirectional traversal is the correct one.