<p>You are given two <strong>non-empty</strong> linked lists representing two non-negative integers. The most significant digit comes first and each of their nodes contains a single digit. Add the two numbers and return the sum 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/2021/04/09/sumii-linked-list.jpg" style="width: 523px; height: 342px;" />
<pre>
<strong>Input:</strong> l1 = [7,2,4,3], l2 = [5,6,4]
<strong>Output:</strong> [7,8,0,7]
</pre>

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

<pre>
<strong>Input:</strong> l1 = [2,4,3], l2 = [5,6,4]
<strong>Output:</strong> [8,0,7]
</pre>

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

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

<p>&nbsp;</p>
<p><strong>Follow up:</strong>&nbsp;Could you solve it without reversing the input lists?</p>

/**
 * 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* t1 = l1, *t2 = l2, *ans, *head;
        ans = new ListNode(0);
        head = ans;
        vector<int> v1, v2;
        
        while(t1){
            v1.push_back(t1->val);
            t1 = t1->next;
        }
        while(t2){
            v2.push_back(t2->val);
            t2 = t2->next;
        }
        
        int n1 = v1.size(), n2 = v2.size();
        
        vector<int> vc(max(n1, n2));
        int sum, carry = 0;
        
        for(int i = n1-1, j = n2-1; i >= 0 || j >= 0; i--, j--){
            if(i < 0){
                sum = v2[j] + carry;
            }else if(j < 0){
                sum = v1[i] + carry;
            }else{
                sum = v1[i] + v2[j] + carry;
            }
            carry = sum / 10;
            sum %= 10;
            vc[max(i, j)] = sum;
        }
        if(carry){
            ans->next = new ListNode(carry);
            ans = ans->next;
        }
        for(int i = 0; i < vc.size(); i++){
            ans->next = new ListNode(vc[i]);
            ans = ans->next;
        }
        
        return head->next;

    }
};
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