61. 链表右移

题目链接：

https://leetcode-cn.com/problems/rotate-list/comments/

解题思路：

先弄成环，然后断链接。

class Solution {
    public ListNode rotateRight(ListNode head, int k) {
        if(head == null) return null;
        ListNode cur = head;
        int n = 1;
        while(cur.next != null){//得到链表的长度
            n++;
            cur = cur.next;
        }
        cur.next = head;//行成循环链表
        int m = n - k % n;
        for(int i = 0; i < m; i++){//到达新链表头节点的前一个节点
            cur = cur.next;
        }
        ListNode newHead = cur.next;
        cur.next = null;
        return newHead;
    }
}