之前写的《每日一题 · 题解》

class Solution {
public:
    ListNode* rotateRight(ListNode* head, int k) {
        if (!head) return head;
        auto p = head;
        auto tail = head;
        int n = 1;
        while (tail->next) {
            tail = tail->next;
            n ++;
        }
        k %= n;
        if (!k) return head;

        auto q = head;
        for (int i = 1; i <= n - k - 1; i ++) {
            q = q->next;
        }
        tail->next = head;
        head = q->next;
        q->next = NULL;
        return head;
    }
};