chal_2.py

class ListNode:
    def __init__(self, val=0, next=None):
        self.val = val
        self.next = next


class Solution:
    def add_two_numbers(self, l1, l2):
        """
        :type l1: ListNode
        :type l2: ListNode
        :rtype: ListNode
        """
        result = ListNode()
        curr_node = result
        carry = 0

        while l1 or l2 or carry:
            digit_1 = l1.val if l1 else 0
            digit_2 = l2.val if l2 else 0
            addition = digit_1 + digit_2 + carry

            carry = addition // 10
            new_digit = addition % 10
            curr_node.next = ListNode(new_digit)
            curr_node = curr_node.next

            l1 = l1.next if l1 else None
            l2 = l2.next if l2 else None

        return result.next


# Test cases
l1 = ListNode(3)
l1.next = ListNode(4)
l1.next.next = ListNode(2)
l2 = ListNode(4)
l2.next = ListNode(6)
l2.next.next = ListNode(5)
solution = Solution()

sol = solution.add_two_numbers(l1, l2)
assert sol.val == 7
assert sol.next.val == 0
assert sol.next.next.val == 8

print(" ", l1.next.next.val, l1.next.val, l1.val)
print("+", l2.next.next.val, l2.next.val, l2.val)
print("---------")
print(" ", sol.next.next.val, sol.next.val, sol.val)