Solution1.py

class Solution:
    def addTwoNumbers(self, l1: ListNode, l2: ListNode) -> ListNode:
        list1 = []
        list2 = []
        
        while l1:
            list1.append(l1.val)
            l1 = l1.next
                
        while l2:
            list2.append(l2.val)
            l2 = l2.next
            
        list1.reverse()
        list2.reverse()
        
        num1 = 0
        num2 = 0
        for i in list1:
            num1 = num1 * 10 + i
        for i in list2:
            num2 = num2 * 10 + i
        
        ans = num1 + num2
        ans = list(str(ans))
        ans.reverse()

        head = ListNode
        l3 = head

        for i in ans:
            l3.next = ListNode(i)
            l3 = l3.next

        return head.next