Deletion of first node in doubly link list

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

Algorithm to delete first node in 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 have only one node i.e. START->NEXT = START
  
  • Set START = NULL
• Else
  
  • Set START = START->NEXT
  • Set START->PREV = NULL
  • Free(TEMP)
• End If;

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

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

 

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

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

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

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

int main(){
 
 NODE *start = NULL;
 
 insertAtLast(&start, 1);
 insertAtLast(&start, 2);
 traverse(&start);
 
 deleteAtFirst(&start);
 traverse(&start);
 
 deleteAtFirst(&start);
 traverse(&start);
 
 deleteAtFirst(&start);
 traverse(&start);
  
 return 0;
}

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

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

void traverse(NODE **start){
 NODE *temp = *start;
 while(temp != NULL){
  printf("%d  ", temp->info);
  temp = temp->next;
 }
 printf("\n");
}

Output:

1  2
2
Error: No nodes

 

Related topics:

• Insert node at first position in Doubly link list
• Insert node at last position in Doubly link list
• Insert node at specific position in Doubly link list
• Delete node at first position in Doubly link list
• Delete node at last position in Doubly link list
• Delete node at specific position in Doubly link list
• Singly Link List
• Circular Link List
• Circular Doubly Link List