Circular Linked List

Circular Linked List is a variation of Linked list in which the first element points to the last element and the last element points to the first element. Both Singly Linked List and Doubly Linked List can be made into a circular linked list.

Singly Linked List as Circular

In singly linked list, the next pointer of the last node points to the first node.

Singly Linked List as Circular Linked List

Doubly Linked List as Circular

In doubly linked list, the next pointer of the last node points to the first node and the previous pointer of the first node points to the last node making the circular in both directions.

Doubly Linked List as Circular Linked List

As per the above illustration, following are the important points to be considered.

·        The last link's next points to the first link of the list in both cases of singly as well as doubly linked list.

·        The first link's previous points to the last of the list in case of doubly linked list.

Basic Operations

Following are the important operations supported by a circular list.

·        insert − Inserts an element at the start of the list.

·        delete − Deletes an element from the start of the list.

·        display − Displays the list.

Insertion Operation

Following code demonstrates the insertion operation in a circular linked list based on single linked list.

Example

insertFirst(data):

Begin

   create a new node

   node -> data := data

   if the list is empty, then

      head := node

      next of node = head

   else

      temp := head

      while next of temp is not head, do

      temp := next of temp

      done

      next of node := head

      next of temp := node

      head := node

   end if

End

Deletion Operation

Following code demonstrates the deletion operation in a circular linked list based on single linked list.

deleteFirst():

Begin

   if head is null, then

      it is Underflow and return

   else if next of head = head, then

      head := null

      deallocate head

   else

      ptr := head

      while next of ptr is not head, do

         ptr := next of ptr

      next of ptr = next of head

      deallocate head

      head := next of ptr

   end if

End

Display List Operation

Following code demonstrates the display list operation in a circular linked list.

display():

Begin

   if head is null, then

      Nothing to print and return

   else

      ptr := head

      while next of ptr is not head, do

         display data of ptr

         ptr := next of ptr

      display data of ptr

   end if

End