2.cpp

/**
 * 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* addTwoNumbers(ListNode* l1, ListNode* l2) {
        ListNode temp={0};
       auto curr = &temp;
       
       auto carry = 0;
        
       while(l1||l2||carry){
           auto a=l1?l1->val:0,b=l2?l2->val:0;
           auto val=carry+a+b;
           curr->next=new ListNode(val%10);
           carry=val/10;
           l1=l1?l1->next:nullptr;
           l2=l2?l2->next:nullptr;
           curr=curr->next;
       } 
        return temp.next;
    }
};