2807. Insert Greatest Common Divisors in Linked List

/**
 * 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* insertGreatestCommonDivisors(ListNode* head)
    {
        if (!head->next) return head;

        ListNode* node1 = head;
        ListNode* node2 = head->next;
        while (node2)
        {
            int gcdVal = gcd(node1->val, node2->val);
            ListNode* gcdNode = new ListNode(gcdVal);

            node1->next = gcdNode;
            gcdNode->next = node2;

            node1 = node2;
            node2 = node2->next;
        }
        return head;
    }
};

• T: $O(n \cdot \log(\min(a, b)))$
• S: $O(1)$