func rotateRight(head *ListNode, k int) *ListNode {
if k == 0 || head == nil || head.Next == nil {
return head
}
n := 1
iter := head
for iter.Next != nil {
iter = iter.Next
n++
}
add := n - k%n
if add == n {
return head
}
iter.Next = head
for add > 0 {
iter = iter.Next
add--
}
ret := iter.Next
iter.Next = nil
return ret
}