Add Two Numbers

You are given two linked lists representing two non-negative numbers. The digits are stored in reverse order and each of their nodes contain a single digit. Add the two numbers and return it as a linked list.

Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)

Output: 7 -> 0 -> 8

Solution:

/**
* Definition for singly-linked list.
* struct ListNode {
*     int val;
*     ListNode *next;
*     ListNode(int x) : val(x), next(NULL) {}
* };
*/
class Solution {
public:
ListNode* addTwoNumbers(ListNode* l1, ListNode* l2) {
ListNode* L = new ListNode(-1);
ListNode* current = L;
int flag = 0;
while(l1 != NULL || l2 != NULL)
{
int val = flag;
if(l1 != NULL)
{
val += l1->val;
l1 = l1->next;
}
if(l2 != NULL)
{
val += l2->val;
l2 = l2->next;
}
if(val >= 10)
{
val %= 10;
flag = 1;
}
else
{
flag = 0;
}
current = current->next = new ListNode(val);
}
if(flag == 1) current = current->next = new ListNode(1);

return L->next;
}
};