61.旋转链表 中等

问题：

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。

示例 1：

输入：head = [1,2,3,4,5], k = 2
输出：[4,5,1,2,3]

示例 2：

输入：head = [0,1,2], k = 4
输出：[2,0,1]

回答：

var rotateRight = function(head, k) {
    if (!head || !head.next || k == 0) return head;
    let slow = head;
    let fast = head;
    let tail = head;
    let len = 1;
    //先获取链表的长度
    while (tail.next) {
        tail = tail.next;
        len++;
    }
    let count = k % len;
    //此时不需要旋转
    if (count == 0) {
        return head;
    }
    for (let i = 0; i < count; i++) {
        fast = fast.next;
    }
    while (fast.next) {
        slow = slow.next;
        fast = fast.next;
    }
    let end = slow.next;
    slow.next = null;
    fast.next = head;
    return end;
};