Deletion in Circular Doubly Linked List at Beginning

by Online Tutorials Library July 22, 2022

Deletion in Circular doubly linked list at beginning

There can be two scenario of deleting the first node in a circular doubly linked list.

The node which is to be deleted can be the only node present in the linked list. In this case, the condition head → next == head will become true, therefore the list needs to be completely deleted.

It can be simply done by assigning head pointer of the list to null and free the head pointer.

in the second scenario, the list contains more than one element in the list, therefore the condition head → next == head will become false. Now, reach the last node of the list and make a few pointer adjustments there. Run a while loop for this purpose

Now, temp will point to the last node of the list. The first node of the list i.e. pointed by head pointer, will need to be deleted. Therefore the last node must contain the address of the node that is pointed by the next pointer of the existing head node. Use the following statement for this purpose.

The new head node i.e. next of existing head node must also point to the last node of the list through its previous pointer. Use the following statement for this purpose.

Now, free the head pointer and the make its next pointer, the new head node of the list.

in this way, a node is deleted at the beginning from a circular doubly linked list.

Algorithm

Step 1: IF HEAD = NULL

Write UNDERFLOW
Go to Step 8
[END OF IF]

Step 2: SET TEMP = HEAD
Step 3: Repeat Step 4 while TEMP -> NEXT != HEAD
Step 4: SET TEMP = TEMP -> NEXT

[END OF LOOP]

Step 5: SET TEMP -> NEXT = HEAD -> NEXT
Step 6: SET HEAD -> NEXT -> PREV = TEMP
Step 7: FREE HEAD
Step 8: SET HEAD = TEMP -> NEXT

C Function

  #include<stdio.h>  #include<stdlib.h>  void create(int);  void deletion_beginning();  struct node  {  int data;  struct node *next;  struct node *prev;  };  struct node *head;  void main ()  {  int choice,item,choice1;  do   {  printf(“1.Append Listn2.Delete Node from beginningn3.Exitn4.Enter your choice?”);  scanf(“%d”,&choice);  switch(choice)  {  case 1:  printf(“nEnter the itemn”);  scanf(“%d”,&item);  create(item);  break;   case 2:  deletion_beginning();  break;   case 3:  exit(0);  break;  default:  printf(“nPlease Enter valid choicen”);  }    }while(choice != 3);  }  void create(int item)  {     struct node *ptr = (struct node *) malloc(sizeof(struct node));     struct node *temp;   if(ptr == NULL)     {         printf(“nOVERFLOWn”);     }     else     {          ptr->data=item;         if(head == NULL)         {             head = ptr;           ptr -> next = head;           ptr -> prev = head;          }         else         {            temp = head;            while(temp->next !=head)            {                temp = temp->next;            }            temp->next = ptr;            ptr ->prev=temp;            head -> prev = ptr;     ptr -> next = head;          }     }       printf(“nNode Insertedn”);  }  void deletion_beginning()  {      struct node *temp;      if(head == NULL)  {  printf(“n UNDERFLOWn”);  }  else if(head->next == head)  {  head = NULL;   free(head);  printf(“nNode Deletedn”);  }  else  {  temp = head;   while(temp -> next != head)  {  temp = temp -> next;  }  temp -> next = head -> next;  head -> next -> prev = temp;  free(head);  head = temp -> next;  printf(“nNode Deletedn”);  }    }  

Output

1.Append List  2.Delete Node from beginning  3.Exit  4.Enter your choice?1    Enter the item  12    Node Inserted  1.Append List  2.Delete Node from beginning  3.Exit  4.Enter your choice?2    Node Deleted

Next TopicDoubly Linked List

Deletion in Circular Doubly Linked List at Beginning

Deletion in Circular doubly linked list at beginning

Algorithm

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