Add two linked lists

add_two.py

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
def build_list_nodes(arr: list, i: int) -> Optional[ListNode]:
    if i < 0: return None
    newNode = ListNode(arr[i])
    newNode.next = build_list_nodes(arr, i - 1)
    return newNode

class Solution:
    def addTwoNumbers(self, l1: Optional[ListNode], l2: Optional[ListNode]) -> Optional[ListNode]:
        current1 = l1
        current2 = l2

        n1 = str(current1.val)
        n2 = str(current2.val)

        while current1 is not None:
            current1 = current1.next
            if current1: n1 += str(current1.val)

        while current2 is not None:
            current2 = current2.next
            if current2: n2 += str(current2.val)

        n1 = n1[::-1]
        n2 = n2[::-1]

        n3 = int(n1)+int(n2)

        arr = [int(d) for d in str(n3)]
        narr = []

        rl = build_list_nodes(arr, len(arr) - 1)

        return rl

gistfile1.txt

Input: l1 = [2,4,3], l2 = [5,6,4]
Output: [7,0,8]
Explanation: 342 + 465 = 807.
Example 2:

Input: l1 = [0], l2 = [0]
Output: [0]
Example 3:

Input: l1 = [9,9,9,9,9,9,9], l2 = [9,9,9,9]
Output: [8,9,9,9,0,0,0,1]