2_AddTwoNumbers.cpp

// 2. Add Two Numbers - https://leetcode.com/problems/add-two-numbers/

/**
 * 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(0);
        ListNode *p = &dummy;
        int carry = 0;
        int sum = 0;
        while (l1 || l2)
        {
            sum = carry;
            if (l1)
                sum += l1->val;
            if (l2)
                sum += l2->val;
            if (sum >= 10)
            {
                carry = sum / 10;
                sum = sum % 10;
            }
            else
            {
                carry = 0;
            }
            p->next = new ListNode(sum);
            p = p->next;
            if (l1)
                l1 = l1->next;
            if (l2)
                l2 = l2->next;
        }
        if (carry)
            p->next = new ListNode(carry);
        return dummy.next;
    }
};