def rotate(self, k):
if self.head and self.head.next:
p = self.head
q = self.head
prev = None
count = 0
while p and count < k:
prev = p
p = p.next
q = q.next
count += 1
p = prev
while q:
prev = q
q = q.next
q = prev
q.next = self.head
self.head = p.next
p.next = None