# Definition for singly-linked list. 
# class ListNode: 
#   def __init__(self, x): 
#     self.val = x 
#     self.next = None 
 
class Solution: 
  # @param head: the list 
  # @param k: rotate to the right k places 
  # @return: the list after rotation 
  def rotateRight(self, head, k): 
    if head is None: 
      return head 
    cur = head 
    count = 1 
    # 计算链表长度 
    while cur.next: 
      cur = cur.next 
      count += 1 
    # 为节省代码量，这里是一个很有技巧的处理：用尾节点链接头结点 
    cur.next = head 
    # 此处，k为cur从尾节点到要断开部分的前驱需走的步数 
    k = count - k % count 
    # 找到前驱 
    while k != 0: 
      cur = cur.next 
      k -= 1 
    # 断开 
    head = cur.next 
    cur.next = None 
    # 因为首尾已经相连，所以直接返回前驱后面的那个节点即可，此处引用为head 
    return head 
    # write your code here