add_lists.py

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
import itertools as it

class IterableListNode(ListNode):
    @classmethod
    def from_ListNode(cls, list_node):
        return cls(list_node.val, list_node.next)

    @classmethod
    def from_iterable(cls, iterable):
        head = None
        node = cls()
        for v in iterable:
            node.next = cls()
            node.next.val = v
            node = node.next
            if head is None:
                head = node
        return head
     
    def __iter__(self):
        self.current_node = self
        return self
    
    def __next__(self):
        if self.current_node is None:
            raise StopIteration
        val = self.current_node.val
        self.current_node = self.current_node.next
        return val
    
    def __add__(self, other):
        def added_digits_iterator(l1, l2):
            take_over = 0
            for x, y in it.zip_longest(l1, l2, fillvalue=0):
                xy = x + y + take_over
                take_over = 1 if xy >= 10 else 0
                yield xy % 10
            if take_over == 1:
                yield 1
                
        return self.from_iterable(added_digits_iterator(self, other))
    
            
def adapt(*list_nodes):
    return [IterableListNode.from_ListNode(ln) for ln in list_nodes]

        
class Solution:
    def addTwoNumbers(self, l1: Optional[ListNode], l2: Optional[ListNode]) -> Optional[ListNode]:
        it_l1, it_l2 = adapt(l1, l2)
        return it_l1 + it_l2