Leetcode: 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.

 1 /**
 2  * Definition for singly-linked list.
 3  * public class ListNode {
 4  *     int val;
 5  *     ListNode next;
 6  *     ListNode(int x) {
 7  *         val = x;
 8  *         next = null;
 9  *     }
10  * }
11  */
12 public class Solution {
13     public ListNode rotateRight(ListNode head, int n) {
14         if (head == null || n == 0) return head;
15         ListNode prev = new ListNode(-1);
16         prev.next = head;
17         int size = 0;
18         ListNode current = prev;
19         ListNode runner = prev;
20         while (current.next != null) {
21             current = current.next;
22             ++size;
23         }
24         current = prev;
25         int shift = n % size;
26         for (; shift > 0; shift--) {
27             runner = runner.next;
28         }
29         while (runner.next != null) {
30             runner = runner.next;
31             current = current.next;
32         }
33         runner.next = prev.next;
34         ListNode newhead = current.next;
35         current.next = null;
36         return newhead;
37     }
38 }