# 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: ListNode, l2: ListNode) -> ListNode:
        ans = None
        end = None
        carry = 0
        while l1 is not None or l2 is not None:
            n1 = 0 if l1 is None else l1.val
            l1 = None if l1 is None else l1.next
            n2 = 0 if l2 is None else l2.val
            l2 = None if l2 is None else l2.next

            new_num = n1 + n2 + carry
            carry = new_num // 10
            new_num %= 10

            # print(n1, n2, new_num, carry)

            if end is not None:
                end.next = ListNode(new_num)
                end = end.next
            else:
                ans = ListNode(new_num)
                end = ans

        if carry != 0:
            end.next = ListNode(carry)

        return ans