/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */
class Solution {
public:
    ListNode* rotateRight(ListNode* head, int k) {
        if (!head) {
            return head;
        }

        int n = 0;
        for (auto a = head; a; a = a->next) {
            ++n;
        }

        k %= n;
        if (!k) {
            return head;
        }

        auto a = head;
        for (int i = 0; i < n - k - 1; ++i) {
            a = a->next;
        }
        auto b = a->next;
        a->next = nullptr;
        auto c = b;
        while (c->next) {
            c = c->next;
        }
        c->next = head;
        return b;
    }
};