Significance of circular linked list

In a circular linked list the next pointer of the last node points to the first node, not to NULL. There is no NULL anywhere in the list.

 last
  |
  v
 [10|*]->[20|*]->[30|*]--+
   ^                      |
   +----------------------+

Significance (uses)

1. Any node can be reached from any other node: starting from any node we can traverse the whole list, which is not possible in an ordinary (linear) singly linked list.
2. Easy access to both ends with one pointer: if we keep a pointer last to the last node, then last->next is the first node. Insertion at the front or the end is O(1).
3. Natural for cyclic problems: round-robin CPU scheduling (the scheduler moves to the next process and returns to the first after the last), Josephus problem, multiplayer turn-taking, music playlists on repeat, buffers.
4. Efficient circular queue: a queue with rear only; enqueue after rear, dequeue rear->next, with no wasted space.
5. No NULL checks for the end: the stop condition is returning to the start node.

Example: round-robin

Processes P1, P2, P3 in a circular list with time slice 4 ms: CPU serves P1, P2, P3, then comes back to P1 automatically by following next. A finished process is simply deleted from the ring.

Traversal must stop when the start node is met again, otherwise it loops forever:

p = last->next;           /* first node */
do { printf("%d ", p->info); p = p->next; } while (p != last->next);