1         public static LinkedListNode ReverseNodesinkGroupOpt(LinkedListNode head, int k)
 2         {
 3             if (k <= 1)
 4                 return head;
 5 
 6             LinkedListNode fakehead = new LinkedListNode();
 7             fakehead.Next = head;
 8             LinkedListNode prev_tail = fakehead;
 9             LinkedListNode curr = head;
10             LinkedListNode next = head;
11             LinkedListNode tail = head;
12 
13             while (curr != null)
14             {
15                 for (int i = 1; i < k; i++)
16                 {
17                     curr = curr.Next;
18                     if (curr == null)
19                         return fakehead.Next;
20                     next = curr.Next;
21                 }
22 
23                 curr.Next = null;
24                 ReverseSignlyLinkedListIterative(tail);
25 
26                 prev_tail.Next = curr;
27                 prev_tail = tail;
28                 tail.Next = next;
29                 curr = next;
30                 tail = next;
31             }
32 
33             return fakehead.Next;
34         }