Circular Linked List in C

November 1, 2023

What is circular linked list in C?

A Circular Linked List in C is a collection of elements connected together with the help of pointers. Such that each node contains a data value and addresses to the next node in the link. Where the last link of the circular Linked list has the address of the first node.

Why circular linked list?

As we know that singly linked list and doubly linked list are already present in there in data structure and algorithm then what is the need of circular linked list?

When we want to access the things in a loop repeatedly. Circular Linked List is ideal so that, whenever we reach the last node we can restart operations again by directly reaching the first node from the last node itself.

Structure of Circular linked list

Circular linked can be of both singly and doubly types. So they can be defined in a program by using the following set of code.

Singly Circular

Doubly Circular

Singly Circular

Singly circular linked list

struct Node {
    int data;
    struct Node *next;
}

Doubly Circular

Doubly circular linked list

struct node   
{  
    struct node *prev, *next; 
    int data; 
}

Advantages of circular linked list in C

Any node of the list can act as the head as the list does not end.
Access to the first node from the last node is easy and time-saving.
Queues can be easily implemented with a circular linked list.
We can traverse the whole list from any node.

Insertion at the beginning in Circular Linked List

Insertion at the end in Circular Linked List

Insertion at the specific position in Circular Linked List

Deletion in Circular Linked List

Split a Circular Linked List in two halves

Operation on circular linked list

We can perform the following operations on a circular linked list.

Insertion
- Inserting at Beginning of the list.
- Inserting at End of the list.
- Insert at a Specific location in the list.
Deletion
- Deleting from the Beginning of the list.
- Deleting from End of the list.
- Deleting a Specific Node from the list

Code For Insertion At The Beginning In Circular Linked List

Run

#include<stdio.h>
#include<stdlib.h>

struct Node
{
  int data;
  struct Node *next;
};

void insertStart (struct Node **head, int data)
{
  struct Node *newNode = (struct Node *) malloc (sizeof (struct Node));
  newNode->data = data;

  // if its the first node being entered
  if (*head == NULL)
    {
      *head = newNode;
      (*head)->next = *head;
      return;
    }

  // if LL already as >=1 node
  struct Node *curr = *head;

  // traverse till last node in LL
  while (curr->next != *head)
    {
      curr = curr->next;
    }
  // assign LL's last node's next as this new node
  curr->next = newNode;

  // assign newNode's next as current head
  newNode->next = *head;

  // change head to this new node
  *head = newNode;
}

void display (struct Node *head)
{
  // if there are no node in LL
  if (head == NULL)
    return;

  struct Node *temp = head;

  //need to take care of circular structure of LL
  do
    {
      printf ("%d ", temp->data);
      temp = temp->next;

    }
  while (temp != head);
  printf ("\n");
}

int main ()
{

  struct Node *head = NULL;

  printf ("Linked List: ");
  insertStart (&head, 6);
  insertStart (&head, 5);
  insertStart (&head, 4);
  insertStart (&head, 3);
  insertStart (&head, 2);
  insertStart (&head, 1);
  display (head);

  return 0;
}

Output

Linked List: 1 2 3 4 5 6

Code For Insertion At The End In Circular Linked List

Run

#include<stdio.h>
#include<stdlib.h>

struct Node
{
  int data;
  struct Node *next;
};

void insertLast (struct Node **head, int data)
{
  struct Node *newNode = (struct Node *) malloc (sizeof (struct Node));
  newNode->data = data;

  // if its the first node being entered
  if (*head == NULL)
    {
      *head = newNode;
      (*head)->next = *head;
      return;
    }

  // if LL already as >=1 node
  struct Node *curr = *head;

  // traverse till last node in LL
  while (curr->next != *head)
    {
      curr = curr->next;
    }

  // assign LL's current last node's next as this new node
  curr->next = newNode;

  // assign this new node's next as current head of LL
  newNode->next = *head;
}

void display (struct Node *head)
{
  // if there are no node in LL
  if (head == NULL)
    return;

  struct Node *temp = head;

  //need to take care of circular structure of LL
  do
    {
      printf ("%d ", temp->data);
      temp = temp->next;

    }
  while (temp != head);
  printf ("\n");
}

int main ()
{

  struct Node *head = NULL;

  printf("Linked List: ");
  insertLast (&head, 0);
  insertLast (&head, 10);
  insertLast (&head, 20);
  insertLast (&head, 30);
  insertLast (&head, 40);
  display (head);

  return 0;
}

Output

Linked List: 0 10 20 30 40

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