43 leetcode - Rotate List

#!/usr/bin/python
# -*- coding: utf-8 -*-
'''
Rotate List
Given a list, rotate the list to the right by k places, where k is non-negative.
For example:
Given 1->2->3->4->5->NULL and k = 2，
return 4->5->1->2->3->NULL.
Subscribe to see which companies asked this question
将单链表循环右移k次，每次移动一个结点。
'''
# Definition for singly-linked list.
class ListNode(object):
def __init__(self, x):
self.val = x
self.next = None

class Solution(object):
def rotateRight(self, head, k):
"""
:type head: ListNode
:type k: int
:rtype: ListNode
"""
if k < 1 or head == None:
return head

length = 1
end = head
while end.next != None:
end = end.next
length += 1

k = k % length  #循环右移length个等于没有移动
if k == 0:
return head

k = length - k
start = head
while k > 1:    #寻找未右移截止点
start = start.next
k -= 1

new_head = start.next#新的起点
start.next = None
end.next = head      #将两个链表链接起来

return new_head

if __name__ == "__main__":
s = Solution()
a = ListNode(1)
b = ListNode(2)
d = ListNode(3)
a.next = b
b.next =d
c = s.rotateRight(a,2)
while c != None:
print c.val
c = c.next