<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) 
    {
        vector<int> ary1;
        vector<int> ary2;
        
        while(l1)
        {
            ary1.push_back(l1->val);
            l1=l1->next;
        }
        while(l2)
        {
            ary2.push_back(l2->val);
            l2=l2->next;
        }
        vector<int> ary3(ary1.size()>ary2.size()?ary1.size():ary2.size());
        int carry=0;
        for(int i=ary1.size()-1,k=ary2.size()-1,j=ary3.size()-1;j>=0;i--,k--,j--)
        {
            if(i>=0&&k>=0)
            {
                ary3[j]=ary1[i]+ary2[k]+carry;
                int temp=ary3[j]%10;
                ary3[j]=ary3[j]/10;
                carry=ary3[j]%10;
                ary3[j]=temp;
            }
            else if(i>=0)
            {
                ary3[j]=ary1[i]+carry;
                int temp=ary3[j]%10;
                ary3[j]=ary3[j]/10;
                carry=ary3[j]%10;
                ary3[j]=temp;
            }
            else if(k>=0)
            {
                ary3[j]=ary2[k]+carry;
                int temp=ary3[j]%10;
                ary3[j]=ary3[j]/10;
                carry=ary3[j]%10;
                ary3[j]=temp;
            }
        }
        ListNode *head=NULL,*newnode;
        for(int i=ary3.size()-1;i>=0;i--)
        {
            newnode=new ListNode(ary3[i]);
            newnode->next=head;
            head=newnode;
        }
        if(carry!=0)
        {
          newnode=new ListNode(carry);
            newnode->next=head;
            head=newnode;  
        }
        return head;
    }
};
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