circular doubly linked list

A circular linked list is a type of linked list in which the last node points to the first, forming a complete circle of nodes. In other words, there is no null element at the end of this variant of the linked list.

We receive some benefits from this little change:

  • A starting point can be any node in the circular linked list.
  • As a result, beginning from any node, the entire list can be traversed.
  • Enqueue and dequeue operations are simple since the circular linked list's end node holds a pointer to the first node.

Overall, this is really helpful in implementing the queue data structure.

It performs similarly to other linked list implementations in terms of performance, with the exception that traversing from the last node to the head node can be done in constant time. This is a linear procedure with traditional linked lists.

Adding Elements

The insertion of new nodes is the first operation we'll go over. We'll have to deal with two scenarios when adding a new element:

  • There are no elements added to the head node, hence it is null. Because there is only one node in this example, we'll make the new node we add the head and tail of the list.
  • The head node isn't null, which means one or more elements have already been added to the list. The old tail should point to the new node in this scenario, and the newly added node will take over as the tail.

The nextNode for tail will point to head in both of the examples above.

Identifying an Element

The next procedure we'll look at is searching to see if an element exists in the list. For this, we'll set the currentNode to a node in the list (typically the head) and traverse the entire list using the nextNode of this node until we discover the required element. Add a new containsNode method that takes the searchValue as a parameter:

Removing an Element

After that, we'll have a look at the remove command. In general, after deleting an element, the prior node's nextNode reference must be updated to point to the nextNode reference of the node that was deleted. However, there are a few exceptions that must be considered:

  • We wish to remove an element from a circular linked list that has only one entry - in this situation, all we need to do is set the head and tail nodes to null.
  • The head node is the one that needs to be removed - we need to make head as the new head nextNode
  • The tail node must be deleted, and the predecessor node of the node to be deleted must be made the new tail node.

Getting Through the List

In this final session, we'll take a look at traversing our circular linked list. We fix the currentNode as head and travel over the complete list using the nextNode of this node, similar to the search and remove procedures.