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Deletion of last node in circular link list

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

Algorithm to delete node at last position in circular link list:

  • Set TEMP1 = START
  • If START != NULL
    • If START->NEXT == NULL
      • START = START->NEXT
      • FREE (TEMP1)
    • Else
      • Traverse the list so that TEMP1 points to last node and TEMP2 points second last node
      • TEMP2->NEXT = NULL
      • FREE (TEMP1)
    • End If;
  • End If;

Function to delete node at last position in circular link list:

 

int deleteLast(NODE **tail){
 NODE *temp;
 int info = -1;
 if(*tail == NULL){
  printf("\nError: List have no node");
 }
 else{
  if(*tail == (*tail)->next){
   temp = *tail;
   *tail = NULL;
   info = temp->info;
   free(temp);
  }
  else{
   temp = (*tail)->next; //temp points to first node
   while(temp->next != *tail){
    temp = temp->next;
   }
   temp->next = (*tail)->next; //points to first node
   info = (*tail)->info; // store the info
   free(*tail); // free last node
   *tail = temp; // update the *tail to second last node
  }
 }
 return info;
}
 

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

 

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

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

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

int main(){
 
 NODE *tail = NULL;
 
 insertAtFirst(&tail, 1); // 1
 insertAtFirst(&tail, 3); // 3 1
 insertAtFirst(&tail, 4); // 4 3 1
 traverse(&tail); // 4 3 1
 printf("\n");
 deleteLast(&tail); // 3 1
 deleteLast(&tail); // 3
 traverse(&tail);
 deleteLast(&tail); // 
 deleteLast(&tail); // no node
 traverse(&tail); // 
 printf("\n");
 
 return 0;
}


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

int deleteLast(NODE **tail){
 NODE *temp;
 int info = -1;
 if(*tail == NULL){
  printf("\nError: List have no node");
 }
 else{
  if(*tail == (*tail)->next){
   temp = *tail;
   *tail = NULL;
   info = temp->info;
   free(temp);
  }
  else{
   temp = (*tail)->next; //temp points to first node
   while(temp->next != *tail){
    temp = temp->next;
   }
   temp->next = (*tail)->next; //points to first node
   info = (*tail)->info; // store the info
   free(*tail); // free last node
   *tail = temp; // update the *tail to second last node
  }
 }
 return info;
}

void traverse(NODE **tail){
 NODE *temp;
 temp = *tail;
 if(*tail){
  do{
   printf("%d  ", temp->next->info);
   temp = temp->next;
  } while(temp != *tail);
 }
}
 
4  3  1
4
Error in Deletion: List have no node

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