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.
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.
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