002_Add_Two_Numbers.py

class ListNode():
    def __init__(self, x):
        self.val = x
        self.next = None
        
class Solution:
    def addTwoNumbers(self, l1: ListNode, l2: ListNode) -> ListNode:
        prev = result = ListNode(None)
        n = 0
        
        while l1 or l2 or n:
            if l1:
                n += l1.val
                l1 = l1.next
                
            if l2:
                n += l2.val
                l2 = l2.next
            
            prev.next = ListNode(n % 10)
            prev = prev.next
            n //= 10
            
        return result.next