思路：双指针，先让快指针走k步，再让两个指针一起走完。把链表头接到链表尾，让慢指针的下一节点成为新链表头，要注意最后三步的处理顺序。

代码

class Solution {
public:
    ListNode* rotateRight(ListNode* head, int k) {
        if (!head || k == 0) return head;
        int n = 0;
        for (auto p = head; p; p = p->next) n ++ ;      //求链表长度

        k %= n;

        auto p = head, q = head;
        while (k -- ) q = q->next;      //1

        while (q->next)                 //2
        {
            q = q->next;
            p = p->next;
        }

        q->next = head;                 //3
        head = p->next;                 //4
        p->next = nullptr;              //5

        return head;
    }
};

参考文献

【手绘漫画】图解LeetCode之旋转链表