2807. Insert Greatest Common Divisors in Linked List

class Solution {
public:
    ListNode* insertGreatestCommonDivisors(ListNode* head) {
        ListNode* f = head;
        if (!head->next) {
            return head;
        }
        ListNode* s = head->next;
        while (s) {
            ListNode* n = new ListNode();
            n->val = gcd(f->val, s->val);
            f->next = n;
            n->next = s;
            f = s;
            s = s->next;
        }
        return head;
    }
};