描述
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->nullptr and k = 2, return 4->5->1->2->3->nullptr.
分析
先遍歷一遍，得出鏈表長度 len，註意 k 可能大於 len，因此令 k% = len。將尾節點 next 指針
指向首節點，形成一個環，接著往後跑 len ? k 步，從這裏斷開，就是要求的結果了。

代碼

 1
 
 public static ListNode rotateRight(ListNode head, int n) {
 2         if (head == null || head.next == null || n == 0)
 3             return head;
 4         ListNode fast = head, slow = head, countlen = head;
 5         ListNode newhead = new ListNode(-1);
 6         int len = 0;
 7 
 8         while
 
 (countlen != null) {
 9             len++;
10             countlen = countlen.next;
11         }
12 
13         n = n % len;
14         if (n == 0)
15             return head;
16         for (int i = 0; i < n; i++) {
17             fast = fast.next; // slow與fast間隔n+1
18         }
19         while (fast.next != null
 
) {
20             slow = slow.next; // slow指向要倒著數的開始點的前一個位置。
21             fast = fast.next;
22 
23         }
24 
25         newhead = slow.next;
26         fast.next = head;
27         slow.next = null;
28 
29         return newhead;
30     }

Rotate List LeetCode Java