STL_Algorithms/addTwoNumbersLinkedList.cpp at master · ashryaagr/STL_Algorithms · GitHub

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/**
 * 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) {
        int sum = 0;
        int carry = 0;
        ListNode *dummy = new ListNode(-1);
        ListNode*temp= dummy;
        while(l1 || l2 || carry){

            sum = 0;
            if(l1){
                sum+= l1->val;
                l1 = l1->next;

            }
            if(l2){
                sum+= l2->val;
                l2 = l2->next;
            }

            sum+= carry;
            carry = sum/10;
            temp->next = new ListNode(sum%10);
            temp = temp->next;

        }
        return dummy->next;

    }
};