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Sudo code to delete 'n' th node of a linked list from the last ?

+4 votes
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Sudo code to delete 'n' th node of a linked list from the last ?
posted Nov 1, 2014 by Ganesh

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1 Answer

+1 vote

Have two pointers – slow and fast and initialize both pointers to head. First move fast pointer to n nodes from head. Now move both pointers one by one until reference pointer reaches end. Now slow pointer is the target node to be deleted and just delete it.

Sample Code

void DeleteNthFromLast(struct node **head, int n)
{
  struct node *slow = *head;
  struct node *fast = *head;
  struct node *pre=null; // to store the previpus pointer of the node to be deleted

  int count = 0;
  if(*head != NULL)
  {
     while( count < n )
     {
        if(fast == NULL)
        {
           printf("%d is greater than the no. of nodes in list", n);
           return;
        }
        fast = fast->next;
        count++;
     } 

     while(fast != NULL)
     {
        pre = slow;
        slow = slow->next;
        fast  = fast->next;
     }

     // Now we got the slow pointer which is the target node lets delete it
     if (pre == null)
     {
         // first node to be deleted so head will change
         *head = (*head)->next;
         free (slow);
     }
     else
     {
         pre->next = slow->next;
         free (slow);
     }

  }
}
answer Nov 2, 2014 by Salil Agrawal
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