61.旋轉鏈表

方法：

記給定的鏈表的長度為n,注意當向右移動的次數k>=n時，僅需要向右移動k mod n次即可，因為每n次移動都會讓鏈表變為原狀

將給定的鏈表連接成環，然后將指定位置斷開

/*** Definition for singly-linked list.* public class ListNode {*     int val;*     ListNode next;*     ListNode() {}*     ListNode(int val) { this.val = val; }*     ListNode(int val, ListNode next) { this.val = val; this.next = next; }* }*/
class Solution {public ListNode rotateRight(ListNode head, int k) {if(k==0 || head == null || head.next == null){return head;}int n = 1;ListNode p = head;while(p.next != null) {p = p.next;n++;}if(k % n == 0 ){return head;}p.next = head;  //最后一個節點指向頭節點，形成一個環形鏈表int add = n - k % n;//找到尾節點while(add > 0){p = p.next;add--;}ListNode t = p.next;p.next = null;return t;}}