Insert node at last position in circular doubly link list

Now we will see how to insert a new node at the last position of doubly link list.

Algorithm for insertion at last position in circular doubly link list:

In this algorithm, START is pointer to first node of list and PTR is the node to be inserted at last. The steps are as follows:

Create new node PTR
Set the info field of PTR
If list is empty i.e. START == NULL
- Set START = PTR
- Set PTR->PREV = PTR
- Set PTR->NEXT = PTR
Else
- Set PTR->NEXT = START
- Set PTR->PREV = START->PREV
- Set START->PREV->NEXT = PTR
- Set START->PREV = PTR
End If;

Function to insert node at last position in circular doubly link list:


void insertAtLast(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;
 }
}

Program to insert at last 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 insertAtLast(NODE **, int);
void traverse(NODE **);

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

void insertAtLast(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;
 }
}

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);
}

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