lec_23.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 *dummy = new ListNode();
    
            ListNode *temp = dummy;
            int carry = 0 ;
    
            while((l1!=NULL || l2!=NULL)|| carry){
    
                int sum = 0;
                if(l1!=NULL){
                    sum+=l1->val;
                    l1 = l1->next;
                }
                if(l2!=NULL){
                    sum+=l2->val;
                    l2 = l2->next;
                }
    
                sum+=carry;
                carry = sum/10;
    
                ListNode *node = new ListNode(sum%10);
                temp ->next = node;
                temp = temp->next;
            }
    
            return dummy->next;
        }
    };