<p>You are given two <strong>non-empty</strong> linked lists representing two non-negative integers. The digits are stored in <strong>reverse order</strong>, and each of their nodes contains a single digit. Add the two numbers and return the sum&nbsp;as a linked list.</p>

<p>You may assume the two numbers do not contain any leading zero, except the number 0 itself.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2020/10/02/addtwonumber1.jpg" style="width: 483px; height: 342px;" />
<pre>
<strong>Input:</strong> l1 = [2,4,3], l2 = [5,6,4]
<strong>Output:</strong> [7,0,8]
<strong>Explanation:</strong> 342 + 465 = 807.
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> l1 = [0], l2 = [0]
<strong>Output:</strong> [0]
</pre>

<p><strong class="example">Example 3:</strong></p>

<pre>
<strong>Input:</strong> l1 = [9,9,9,9,9,9,9], l2 = [9,9,9,9]
<strong>Output:</strong> [8,9,9,9,0,0,0,1]
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li>The number of nodes in each linked list is in the range <code>[1, 100]</code>.</li>
	<li><code>0 &lt;= Node.val &lt;= 9</code></li>
	<li>It is guaranteed that the list represents a number that does not have leading zeros.</li>
</ul>

/**
 * 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) {

        bool carry = false;

        ListNode* firstNode = l1;

        ListNode* lastl1Node = l1;

        while (l1 != NULL || l2 != NULL) {
            if (l1 != NULL && l2 != NULL) {
                int nodeSum = l1->val + l2->val + carry;
                if (nodeSum > 9) {
                    l1->val = (nodeSum) % 10;
                    carry = true;
                } else {
                    l1->val = nodeSum;
                    carry = false;
                }
                if (l1->next == NULL) {
                    lastl1Node = l1;
                }
                l1 = l1->next;
                l2 = l2->next;
            } else if (l1 != NULL || l2 != NULL) {
                if (l1 != NULL) {
                    if (l1->val + carry > 9) {
                        l1->val = 0;
                    } else {
                        l1->val += carry;
                        carry = false;
                    }

                    if (l1->next == NULL) {
                        lastl1Node = l1;
                    }
                    l1 = l1->next;
                } else {
                    ListNode* newNode = new ListNode();
                    lastl1Node->next = newNode;
                    if (l2->val + carry > 9) {
                        newNode->val = 0;
                    } else {
                        newNode->val = l2->val + carry;
                        carry = false;
                    }
                    l2 = l2->next;
                    lastl1Node = lastl1Node->next;
                }
            }
        }
        if (carry) {
            ListNode* newNode = new ListNode();
            lastl1Node->next = newNode;
            newNode->val = 1;
            lastl1Node = lastl1Node->next;
        };

        cout << lastl1Node->val << endl;

        return firstNode;
    }
};
76800