class Solution{
    public: 
        ListNode* addTwoNumbers(ListNode* l1, ListNode* l2){
            ListNode* dummyhead = new ListNode(0);
            ListNode* tail = dummyhead;
            bool carry = 0;

            while(l1 || l2|| carry){
                int digit1 = (l1!=nullptr) ? l1->val : 0;
                int digit2 = (l2!=nullptr) ? l2->val : 0;

                int sum = digit1+digit2+carry;
                int digit = sum%10;
                carry = sum/10;

                ListNode* newnode = new ListNode*(digit);
                tail->next = newnode;
                tail = tail->next;

                l1 = (l1!=nullptr) ? l1=>next : nullptr;
                l2 = (l2!=nullptr) ? l2->next : nullptr;
            }
            ListNode* result = dummyhead->next;
            delete dummyhead;
            return result;
        }
}