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Deletion of node at specific position N in doubly link list

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

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

In this algorithm, START 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)
    • Invalid deletion
  • Else if POS == 1
    • insertAtFirst()
  • Else
    • TEMP = START
    • Traverse the list so that TEMP points to POS-1 th node
    • If TEMP->NEXT->NEXT == NULL
      • TEMP->NEXT = NULL
    • Else
      • TEMP->NEXT = TEMP->NEXT->NEXT
      • TEMP->NEXT->PREV = TEMP
    • End If
  • End If

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


int deleteAtPosition(NODE **start, int pos){
 NODE *temp, *temp2 = *start;
 int info = -1;
 if(pos < 1 || *start == NULL){
  printf("\nError : Invalid position");
  return -1;
 }
 if(pos == 1){
  info = (*start)->info;
  if((*start)->next == NULL){
   *start = NULL;
  }
  else{
   *start = (*start)->next;
   (*start)->prev = NULL;
  }
  free(temp2);
 }
 else{
  temp = *start;
  for(int i = 2; i < pos; i++){
   temp = temp->next;
   if(temp->next == NULL){
    printf("\nError: Invalid position\n");
    return -1;
   }
  }
  temp2 = temp->next;
  info = temp2->info;
  if(temp->next->next == NULL){
   temp->next = NULL;
  }
  else{
   temp->next = temp->next->next;
   temp->next->prev = temp;
  }
  free(temp2);
 }
 return info;
}
 

Program to delete node at position 'N' in doubly link list:


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

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

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

int main(){
 NODE *start = NULL;
 
 insertAtLast(&start, 1);
 insertAtLast(&start, 2);
 insertAtLast(&start, 3);
 insertAtLast(&start, 4);
 insertAtLast(&start, 5);
 
 deleteAtPosition(&start, 1);
 traverse(&start);
 
 deleteAtPosition(&start, 2);
 traverse(&start);
 
 deleteAtPosition(&start, 3);
 traverse(&start);
 
 deleteAtPosition(&start, 3);
 traverse(&start);
 return 0;
}

int deleteAtPosition(NODE **start, int pos){
 NODE *temp, *temp2 = *start;
 int info = -1;
 if(pos < 1 || *start == NULL){
  printf("\nError : Invalid position");
  return -1;
 }
 if(pos == 1){
  info = (*start)->info;
  if((*start)->next == NULL){
   *start = NULL;
  }
  else{
   *start = (*start)->next;
   (*start)->prev = NULL;
  }
  free(temp2);
 }
 else{
  temp = *start;
  for(int i = 2; i < pos; i++){
   temp = temp->next;
   if(temp->next == NULL){
    printf("\nError: Invalid position\n");
    return -1;
   }
  }
  temp2 = temp->next;
  info = temp2->info;
  if(temp->next->next == NULL){
   temp->next = NULL;
  }
  else{
   temp->next = temp->next->next;
   temp->next->prev = temp;
  }
  free(temp2);
 }
 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:
2  3  4  5
2  4  5
2  4

Error: Invalid position
2  4
 

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