<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.
# class ListNode:
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution:
    def addTwoNumbers(self, l1: Optional[ListNode], l2: Optional[ListNode]) -> Optional[ListNode]:
        prev = None 
        temp = l1
        while temp :
            temp2 = temp.next
            temp.next = prev
            prev = temp
            temp = temp2
        temp1 = prev
        prev = None
        temp = l2
        while temp :
            temp2 = temp.next
            temp.next = prev
            prev = temp
            temp = temp2
        temp2 = prev
        head = ListNode(-1)
        node = head
        count = 0
        while temp1 or temp2 :
            val = count
            count = 0
            if temp1 :
                val += temp1.val
                temp1 = temp1.next
            if temp2 :
                val += temp2.val
                temp2 = temp2.next
            if val // 10 > 0 :
                count = 1 
                val = val % 10
            node.next = ListNode(val)
            node = node.next
        if count != 0 :
            node.next = ListNode(count)
            node = node.next
        node.next = None
        prev = None 
        temp = head.next
        while temp :
            temp2 = temp.next
            temp.next = prev
            prev = temp
            temp = temp2
        return prev
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