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Insert node at specific position N in circular link list

Now we will see how to insert a new node at position N in circular link list.

Algorithm for insertion at position N in circular link list:

In this algorithm, TAIL is pointer to the last node of the list and PTR is node to be inserted. The step are as below :
  • Create new node PTR
  • Set the info field of PTR
  • If list have no nodes i.e. (TAIL == NULL)
    • If (POS == 1)
      • Set PTR->NEXT = PTR
      • Set TAIL = PTR
    • Else
      • Invalid POS. Node can't be inserted
    • End If;
  • Else if (POS == 1) (Now list is not empty also)
    • Set PTR->NEXT = TAIL->NEXT
    • Set TAIL->NEXT = PTR
  • Else
    • Set TEMP = TAIL->NEXT
    • Traverse the list for (POS-1)th node of list into TEMP
    • If TEMP == TAIL
      • Set PTR->NEXT = TAIL->NEXT
      • Set TAIL->NEXT = PTR
      • Set TAIL = PTR
    • Else
      • Set PTR->NEXT = TEMP->NEXT
      • Set TEMP->NEXT = PTR
    • End If;
  • End If;



Function to insert node at position N in circular link list:


void insertAtPosition(NODE **tail, int info, int pos){
 NODE *ptr = (NODE*) malloc(sizeof(NODE));
 ptr->info = info;
 NODE *temp;
 if(pos < 1){ 
  printf("Error: Position can't be 0 or negative\n"); 
  return; 
 } 
 if(*tail == NULL){ 
  if(pos == 1){ 
   ptr->next = ptr;
   *tail = ptr;
  }
  else{
   printf("\nList is empty. Invalid position\n");
  }
 }
 else if(pos == 1){
  ptr->next = (*tail)->next;
  (*tail)->next = ptr;
 }
 else{
  temp = (*tail)->next;
  for( int i = 2; i < pos; i++){ temp = temp->next;
   if(temp == (*tail)->next){
    printf("\nError: Invalid position\n");
    return;
   }
  }
  if(temp == *tail){
   ptr->next = (*tail)->next;
   (*tail)->next = ptr;
   *tail = ptr;
  }
  else{
   ptr->next = temp->next;
   temp->next = ptr;
  }
 }
}

Program to insert at position N in the singly link list:


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

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

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

int main(){
 
 NODE *tail = NULL;
 
 insertAtFirst(&tail, 1);
 insertAtFirst(&tail, 3);
 insertAtFirst(&tail, 4);
 traverse(&tail);

 insertAtPosition(&tail, 9, 0);
 traverse(&tail);
 
 insertAtPosition(&tail, 9, 1);
 traverse(&tail);
 
 insertAtPosition(&tail, 44, 3);
 traverse(&tail);
 
 insertAtPosition(&tail, 89, 6);
 traverse(&tail);
 
 insertAtPosition(&tail, 89, 8);
  
 return 0;
 
}

void insertAtPosition(NODE **tail, int info, int pos){
 NODE *ptr = (NODE*) malloc(sizeof(NODE));
 ptr->info = info;
 NODE *temp;
 if(pos < 1){ 
  printf("Error: Position can't be 0 or negative\n"); 
  return; 
 } 
 if(*tail == NULL){ 
  if(pos == 1){ 
   ptr->next = ptr;
   *tail = ptr;
  }
  else{
   printf("\nList is empty. Invalid position\n");
  }
 }
 else if(pos == 1){
  ptr->next = (*tail)->next;
  (*tail)->next = ptr;
 }
 else{
  temp = (*tail)->next;
  for( int i = 2; i < pos; i++){ temp = temp->next;
   if(temp == (*tail)->next){
    printf("\nError: Invalid position\n");
    return;
   }
  }
  if(temp == *tail){
   ptr->next = (*tail)->next;
   (*tail)->next = ptr;
   *tail = ptr;
  }
  else{
   ptr->next = temp->next;
   temp->next = ptr;
  }
 }
}

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  1
Error: Position can't be 0 or negative
4  3  1
9  4  3  1
9  4  44  3  1
9  4  44  3  1  89

Error: Invalid position

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