Leetcode/Add Two Numbers.cpp at main · mahfuj10/Leetcode · 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)
    {
        ListNode *head = NULL;
        ListNode *temp = NULL;

        int carry = 0;

        while (l1 != NULL || l2 != NULL)
        {
            int sum = carry;
            if (l1 != NULL)
            {
                sum += l1->val;
                l1 = l1->next;
            }

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

            ListNode *node = new ListNode(sum % 10);
            carry = sum / 10;

            if (temp == NULL)
            {
                temp = head = node;
            }
            else
            {
                temp->next = node;
                temp = temp->next;
            }

            if (carry > 0)
            {
                temp->next = new ListNode(carry);
            }
        }
        return head;
    }
};