CareerCup

I used 3 pointers. Not sure if you can do it with two. If anyone has any suggestions please let me know! handles even # of nodes, odd # of nodes, 0, 1, 2 nodes.

void swap_every_two(node **head) {
  node *current = *head;
  node *next = NULL;
  node *prev = NULL;
  if (head == NULL)
    return;
  if (*head == NULL) /* no elements */
    return;
  if ((*head)->next == NULL) /* only one element */
    return;
  *head = current->next; /* update the head pointer */
  next = current->next;
  current->next = next->next;
  next->next = current;
  prev = current;
  current = current->next;
  while (current != NULL && current->next != NULL) {
    next = current->next;
    current->next = next->next;
    next->next = current;
    prev->next = next;
    prev = current;
    current = current->next;
  }

}

1.break link list into two parts.evenPart 2->4->6 and oddPart 1->3->5->7.
2.now built a link list as even->odd->even->odd->even->odd : 2->1->4->3->6->5

Recursive solution:

void swappairs(node **head)
{
        if(head==NULL ||*head==NULL)
                return;
        if((*head)->next==NULL)
                return;
        node *current = *head;
        *head=(*head)->next;
        current->next=(*head)->next;
        (*head)->next=current;
        swappairs(&(current->next));
}

void swapNodes(Node **head) {
	if(!*head)
		return;
	int first = 1;
	Node *newHead;
	while((*head)->next) {
		Node *tmp = *head;
		Data data = (*head)->data;
		displayData(data);
		Node *next = (*head)->next;
		Node *after = NULL;
		if(next->next)
			after = next->next;
		(*head)->data = next->data;
	    (*head) = next;
	    next->data = data;	
		next = tmp;
		next->next = (*head);
		if(first) {
			newHead = next;
			first = 0;
		}
		(*head)->next = after;
		if(after)
			(*head) = after;
	}
	*head = newHead;
}

lnode *swap_two(lnode *start)
{
lnode *ret;
lnode *next_two;

// Terminate Recursion
if (start == NULL || start->next == NULL)
return (start);

next_two = start->next->next;
ret = start->next;
start->next->next = start;
start->next = swap_two(next_two);

return (ret);
}

Functions return linked list in such order.