static void Main(string[] args)
{
ListNode lN = new ListNode(1);
lN.next = new ListNode(2);
lN.next.next = new ListNode(3);
lN.next.next.next = new ListNode(4);
lN.next.next.next.next = new ListNode(5);
SwapPairs(lN);
}
public static ListNode SwapPairs(ListNode head)
{
if (head == null)
{
return null;
}
else if (head.next == null)
{
return head;
}
var prev = head;
var next = head.next;
var counter = head.next.next;
next.next = prev;
prev.next = counter;
head = next;
var temp = prev;
while (counter != null)
{
if (temp.next.next == null)
{
return head;
}
else
{
prev = counter;
next = counter.next;
counter = counter.next.next;
next.next = prev;
prev.next = counter;
temp.next = next;
}
temp = prev;
}
return head;
}
