What is a circular doubly linked list and what is a common use-case?

• A. A circular doubly linked list has only forward pointers and uses as a stack.
• B. A circular doubly linked list has next and prev pointers with head and tail connected in a loop; used in round-robin scheduling or MRU caches.
• C. A circular doubly linked list is the same as a standard singly linked list.
• D. There is no such thing as a circular doubly linked list.

Answer: (B)

A circular doubly linked list is a sequence of nodes where each node has both a next and a previous pointer, and the ends connect to form a loop so the next pointer of the last node points back to the first node and the previous pointer of the first node points to the last. This setup lets you move forward or backward through the list indefinitely without hitting a null terminator, and you can insert or remove nodes in constant time when you have references to the neighboring nodes.

A common use-case is round-robin scheduling, where you cycle through items in order and automatically wrap around after the last one. The circular structure makes this wrap-around seamless, so you can keep advancing to the next element without special-end handling. It also supports efficient reordering, such as moving recently used items around in a cache, which is why this structure is often associated with scenarios that require easy cyclic traversal and quick updates.