给你一个链表的头节点head，旋转链表，将链表每个节点向右移动 k个位置。

    1. 输入：head = [1,2,3,4,5], k = 2
    2. 输出：[4,5,1,2,3]
    1. var rotateRight = function (head, k) {
    2.     if (!head || !head.next || !k) return head
    3.     let n = 1
    4.     let cur = head
    5.     while (cur.next) {
    6.         n++
    7.         cur = cur.next
    8.     }
    9.     // 取余，防止多次旋转
    10.     let add = n - k % n
    11.     // 建立环形
    12.     cur.next = head
    13.     while (add) {
    14.         add--
    15.         cur = cur.next
    16.     }
    17.     const res = cur.next
    18.     // 切断环形链接
    19.     cur.next = null
    20.     return res
    21. }