AddTwoNumbers.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* c1 = l1;
        ListNode* c2 = l2;
        ListNode* ans = new ListNode(0);
        ListNode* temp = ans;
        int sum = 0;
        while(c1!=NULL || c2!=NULL){
            sum = sum/10;
            if(c1!=NULL){
                sum+=c1->val;
                c1 = c1->next;
            }
            if(c2!=NULL){
                sum+=c2->val;
                c2 = c2->next;
            }
            temp->next = new ListNode(sum%10);
            temp=temp->next;
        }
        if(sum/10 > 0){
            temp->next = new ListNode(1);
        }
        return ans->next;
    }
};