<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* reverseLinked(ListNode *head){
    if(head==nullptr) return nullptr;
        ListNode *p =nullptr, *curr, *q;
        curr=head;
        q=head->next;
        while(q!=nullptr){
curr->next=p;
p=curr;
curr=q;
q=q->next;
        }
        curr->next=p;
        p=curr;
return p;
}
    ListNode* addTwoNumbers(ListNode* l1, ListNode* l2) {
if(l1==nullptr||l2==nullptr) return nullptr;
       ListNode *p=reverseLinked(l1);
       ListNode *q=reverseLinked(l2);
       ListNode *curr=new ListNode(0);
ListNode *temp=curr;
int num=0;
while(p!=nullptr|| q!=nullptr){
    int a=(p!=nullptr)?p->val:0;
    int b=(q!=nullptr)?q->val:0;
    int sum=a+b+num;
    num=sum/10;
    temp->next=new ListNode(sum%10);
    temp=temp->next;
    if(p!=nullptr) p=p->next;
    if(q!=nullptr) q=q->next;
}
if(num >0){
    temp ->next=new ListNode(num);
}

                return reverseLinked(curr->next);

            }
};
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