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Deletion of node at specific position N in circular link list

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

Algorithm to delete node at position 'N' in circular link list:

In this algorithm, TAIL points to last node of the link list and POS is position where the new node to be deleted. The steps are as follows:
  • Initialize TEMP and TEMP2
  • If list have no node or position is less than one  (TAIL == NULL or POS < 1)
    • Node cannot be deleted
  • Else
    • If (POS == 1)
      • If list have one node   (TAIL->NEXT == TAIL)
        • Delete TAIL   (TAIL = NULL)
      • Else
        • Delete the first node   (TAIL->NEXT = TAIL->NEXT->NEXT)
      • End If;
    • Else
      • Set TEMP = TAIL->NEXT   (TEMP now points to first node)
      • Traverse the list for (POS-1)th node using TEMP
        • If node to be deleted is last node i.e. (TEMP->NEXT == TAIL)
          • Set TAIL = TEMP
        • End If;
      • Set TEMP->NEXT = TEMP->NEXT->NEXT
    • End If;
  • End If;
 

 


Function to delete node at position 'N' in circular link list:


int deleteAtPosition(NODE **tail, int pos){
 NODE *temp, *temp2;
 int info = -1;
 if((*tail == NULL) || pos < 1){
  printf("\nERROR: List have no nodes or invalid position");
 }
 else{
  if(pos == 1){
   if((*tail)->next == *tail){
    info = (*tail)->info;
    free(*tail);
    *tail = NULL;//
   }
   else{
    temp2 = (*tail)->next;
    info = temp2->info;
    (*tail)->next = (*tail)->next->next;//
    free(temp2);
   }
  }
  else{
   temp = (*tail)->next;
   for( int i = 1; i < (pos-1); i++){
    temp = temp->next;
    if(temp == *tail){
     printf("\nError: Cannot be deleted, invalid position");
     return -1;
    }
   }
   if(temp->next == *tail){
    *tail = temp;
   }
   temp2 = temp->next;
   info = temp2->info;
   temp->next = temp->next->next;//
   free(temp2);
  }
 }
 return info;
}
 

Program to delete node at position 'N' in 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 deleteAtPosition(NODE **, int);
void traverse(NODE **);

int main(){
 
 NODE *tail = NULL;
 
 insertAtFirst(&tail, 1); // 1
 insertAtFirst(&tail, 2); // 2 1
 insertAtFirst(&tail, 3); // 3 2 1
 insertAtFirst(&tail, 4); // 4 3 2 1
 traverse(&tail); // 4 3 2 1
 
 deleteAtPosition(&tail, 4);
 traverse(&tail); // 4 3 2
 
 deleteAtPosition(&tail, 1); 
 traverse(&tail); // 3 2
 
 deleteAtPosition(&tail, 3); // invalid position
 printf("\n");
 traverse(&tail); // 3 2
 
 return 0;
}

int deleteAtPosition(NODE **tail, int pos){
 NODE *temp, *temp2;
 int info = -1;
 if((*tail == NULL) || pos < 1){
  printf("\nERROR: List have no nodes or invalid position");
 }
 else{
  if(pos == 1){
   if((*tail)->next == *tail){
    info = (*tail)->info;
    free(*tail);
    *tail = NULL;//
   }
   else{
    temp2 = (*tail)->next;
    info = temp2->info;
    (*tail)->next = (*tail)->next->next;//
    free(temp2);
   }
  }
  else{
   temp = (*tail)->next;
   for( int i = 1; i < (pos-1); i++){
    temp = temp->next;
    if(temp == *tail){
     printf("\nError: Cannot be deleted, invalid position");
     return -1;
    }
   }
   if(temp->next == *tail){
    *tail = temp;
   }
   temp2 = temp->next;
   info = temp2->info;
   temp->next = temp->next->next;//
   free(temp2);
  }
 }
 return info;
}

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;
 }
}

void traverse(NODE **tail){
 NODE *temp;
 temp = *tail;
 if(*tail){
  do{
   printf("%d  ", temp->next->info);
   temp = temp->next;
  } while(temp != *tail);
  printf("\n");
 }
}
 
4  3  2  1
4  3  2
3  2
Error: Cannot be deleted, invalid position
3  2

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