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Deletion of first node in circular doubly list

Now we will see how to delete node at first position in circular doubly link list.

Algorithm to delete first node in circular doubly link list:

In this algorithm, START is pointer to the first node of doubly list. The steps are below:
  • Declare TEMP = START
  • If list has no node i.e. [START == NULL]
    • Deletion not possible as no node in the list
  • Else If list have only one node i.e. START->NEXT = START
    • Set START = NULL
  • Else
    • Set START->NEXT->PREV = START->PREV
    • Set START->PREV->NEXT = START->NEXT
    • Set START = START->NEXT
  • Free(TEMP)
  • End If;


Function to delete node at first position in circular doubly link list:


int deleteAtFirst(NODE **start){
 NODE *temp = *start;
 int info = -1;
 if(*start == NULL){
  printf("\nError: No nodes\n");
 }
 else{
  if((*start)->next == *start){
   *start = NULL;
  }
  else{
   (*start)->next->prev = (*start)->prev;
   (*start)->prev->next = (*start)->next;
   *start = (*start)->next;
  }
  info = temp->info;
  free(temp);
 }
 return info;
}
 

Program to delete node at first position in the circular doubly link list:


#include <stdio.h>
#include <malloc.h>

#include 
#include 

typedef struct node{
 struct node *prev;
 int info;
 struct node *next;
} NODE;

void insertAtFirst(NODE **, int);
int deleteAtFirst(NODE **);
void traverse(NODE **);

int main(){
 NODE *start = NULL;
 deleteAtFirst(&start);
 insertAtFirst(&start, 3);
 traverse(&start);
 deleteAtFirst(&start);
 insertAtFirst(&start, 24);
 insertAtFirst(&start, 4);
 traverse(&start);
 deleteAtFirst(&start);
 traverse(&start);
 return 0;
}

void insertAtFirst(NODE **start, int info){
 NODE *ptr = (NODE*) malloc(sizeof(NODE));
 ptr->info = info;
 if(*start == NULL){
  *start = ptr;
  ptr->next = ptr;
  ptr->prev = ptr;
 }
 else{
  ptr->next = *start;
  ptr->prev = (*start)->prev;
  (*start)->prev->next = ptr;
  (*start)->prev = ptr;
  *start = ptr;
 }
}

int deleteAtFirst(NODE **start){
 NODE *temp = *start;
 int info = -1;
 if(*start == NULL){
  printf("\nError: No nodes\n");
 }
 else{
  if((*start)->next == *start){
   *start = NULL;
  }
  else{
   (*start)->next->prev = (*start)->prev;
   (*start)->prev->next = (*start)->next;
   *start = (*start)->next;
  }
  info = temp->info;
  free(temp);
 }
 return info;
}

void traverse(NODE **start){
 NODE *ptr = *start;
 if(ptr == NULL){
  printf("\nEmpty list\n");
  return;
 }
 while( ptr->next != *start ){
  printf("%d  ",ptr->info);
  ptr = ptr->next;
 }
 printf("%d\n",ptr->info);
}
Output:
Error: No nodes
3
4 24
24

Error: No nodes
 

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