```
# Definition for singly-linked list.
# class ListNode:
# def __init__(self, x):
# self.val = x
# self.next = None
class Solution:
# @param head, a ListNode
# @param k, an integer
# @return a ListNode
def rotateRight(self, head, k):
if not head or k == 0:
return head
slow = fast = head
length = 1
while k and fast.next:
fast = fast.next
length += 1
k -= 1
if k != 0:
k = (k + length - 1) % length # original k % length
return self.rotateRight(head, k)
else:
while fast.next:
fast = fast.next
slow = slow.next
return self.rotate(head, fast, slow)
def rotate(self, head, fast, slow):
fast.next = head
head = slow.next
slow.next = None
return head
```