在链表中的第n个位置插入元素 - C.

Question

my program shows list is empty. I think I'm making mistake on re-linking the nodes to the head. Help me figure it out.

void insert(struct node** headRef, int index, int Data)
{
  int i, distanceFromHead = 1;
  struct node* head = *headRef;
  struct node* temp1 = (struct node*)malloc(sizeof(struct node)); //node to be inserted.
  temp1->data = Data;
  if(index == 0)
  {
    temp1->next = head;
    head = temp1;
    return;
  }
  while(head != NULL)
  {
    if(distanceFromHead == index)
    {
        temp1->next = head->next;
        head->next = temp1;
        *headRef = head;
        return;
    }
    head = head->next;
    distanceFromHead++;
  }

}

Answer 1

You're using head to iterate through the linked list and if index matched with distance then updating headref .

Problem is *headRef = head in while..if

And in if(index == 0) assign temp1 to *headref ie *headref=temp1

Answer 2

Your have two conditions:

• finding the postion for insertion in the Linked list
• not falling off the end of the Linked List

And, of course, you have to assign to *headRef , not to some local pointer variable. And you should not call malloc before you are absolutely sure you really need the memory.

You can combine the two conditions in a single loop:

---

void insert1(struct node **headRef, int index, int Data)
{
  struct node *temp1;
  int distanceFromHead = 0;

  for( ; *head; head = &(*head)->next) {
    if(distanceFromHead == index) break;
    distanceFromHead++;
  }

  if (distanceFromHead != index) return; // index not found: list too short

  temp1 = malloc(sizeof *temp1); //node to be inserted.
  temp1->data = Data;
  temp1->next = *head;
  *head = temp1;
}

You dont need the distanceFromHeadvarable; you could just as well decrement the index:

void insert2(struct node **headRef, int index, int Data)
{
  struct node *temp1;

  for( ; *head; head = &(*head)->next) {
    if(!index) break;
    index--;
  }
  if (index) return; // index not found: list too short

  temp1 = malloc(sizeof *temp1); //node to be inserted.
  temp1->data = Data;
  temp1->next = *head;
  *head = temp1;
}

Now, the test for index!=0 is repeated after the loop. This can be avoided by moving the insertion inside the loop, and jumping out afterwards:

void insert3(struct node **headRef, int index, int Data)
{

  for( ; *head; head = &(*head)->next) {
    struct node *temp1;
    if(index--) continue;

    temp1 = malloc(sizeof *temp1); //node to be inserted.
    temp1->data = Data;
    temp1->next = *head;
    *head = temp1;
    break; // or : return;
  }

  return;
}