C# 代码

public class Solution {
    public ListNode RotateRight(ListNode head, int k) {
        if(head == null) return head;
        ListNode dummy = new ListNode(0, head);

        // 求链表长度
        int length = 0;
        ListNode current = dummy.next;
        while (current != null){
            length++;
            current = current.next;
        }

        k = k % length;
        if (k == 0) return head;
        ListNode fast = dummy;
        ListNode slow = dummy;

        while (k-- >0){
            fast = fast.next;
        }

        // 快慢指针求出断开位置
        while (fast.next != null){
            fast = fast.next;
            slow = slow.next;
        }

        // 链表结尾连接到头节点
        fast.next = head;
        // 新的头节点是slow节点的下一个节点
        ListNode newHead = slow.next;
        // 一定要断开slow节点, 否则会报OOM
        slow.next = null;
        return newHead;
    }
}