答案

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) {
 *         val = x;
 *         next = null;
 *     }
 * }
 */
public class Solution {
    public ListNode rotateRight(ListNode head, int n) {
        if(n<=0||head==null||head.next==null)
        {
            return head;
        }
        ListNode first=head;
        ListNode second=head;
        int N=0;
        for(ListNode p=head;p!=null;p=p.next)
        {
            N++;
        }
        n=n%N;
        if(n==0)
        {
            return head;
        }
        while(n>=2&&second!=null)
        {
            second=second.next;
            n--;
        }
        if(second==null)
        {
            return head;
        }
        for(;second.next!=null;first=first.next,second=second.next);
        second.next=head;
        for(second=head;second!=null;second=second.next)
        {
            if(second.next==first)
            {
                second.next=null;
            }
        }
        return first;
    }
}