LeetCode 61. 旋转链表

给定一个链表，旋转链表，将链表每个节点向右移动 k 个位置，其中 k 是非负数。

示例 1:
输入: 1->2->3->4->5->NULL, k = 2
输出: 4->5->1->2->3->NULL
解释:
向右旋转 1 步: 5->1->2->3->4->NULL
向右旋转 2 步: 4->5->1->2->3->NULL

示例 2:
输入: 0->1->2->NULL, k = 4
输出: 2->0->1->NULL
解释:
向右旋转 1 步: 2->0->1->NULL
向右旋转 2 步: 1->2->0->NULL
向右旋转 3 步: 0->1->2->NULL
向右旋转 4 步: 2->0->1->NULL

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution:
    def rotateRight(self, head: ListNode, k: int) -> ListNode:
        if head is None or head.next is None :
            return head 
        cnt = 1 
        tmp = head 
        while tmp.next is not None:
            tmp = tmp.next 
            cnt += 1
        k = k%cnt 
        #print(cnt,k)
        if k==0:
            return head 
        tail1 = head 
        tail2 = head 
        for i in range(k):
            tail2 = tail2.next 
        while tail2.next is not None:
            tail1 = tail1.next 
            tail2 = tail2.next
        #print(head.val,tail1.val,tail2.val)
        tail2.next = head  
        head = tail1.next 
        tail1.next = None 
        return head