LeetCode 2. Add two numbers

Here are two for you Non empty The linked list of , Represents two nonnegative integers . Each of them is based on The reverse Stored in , And each node can only store a Numbers .

Please add up the two numbers , And returns a linked list representing sum in the same form .

You can assume that in addition to the numbers 0 outside , Neither of these numbers 0 start .

Input ：l1 = [2,4,3], l2 = [5,6,4]
Output ：[7,0,8]
explain ：342 + 465 = 807.
Example 2：
Input ：l1 = [0], l2 = [0]
Output ：[0]
Example 3：
Input ：l1 = [9,9,9,9,9,9,9], l2 = [9,9,9,9]
Output ：[8,9,9,9,0,0,0,1]

/** * 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* ret = new ListNode(0);
        ListNode* cur = ret;

        int sum = 0;
        while(1)
        {
    
            if(l1 != nullptr)
            {
    
                sum += l1->val;
                l1 = l1->next;
            }

            if(l2 != nullptr)
            {
    
                sum += l2->val;
                l2 = l2->next;
            }
            cur->val = sum % 10;
            sum /= 10;
            if(l1 != nullptr || l2 != nullptr || sum)
                cur = (cur->next = new ListNode(0));
            else
                break;
        }
        return ret;
    }
};