#2. Add Two Numbers

You are given two non-empty linked lists representing two non-negative integers. The digits are stored in reverse order, and each of their nodes contains a single digit. Add the two numbers and return the sum as a linked list. You may assume the two numbers do not contain any leading zero, except the number 0 itself.  

Example 1:
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]

# 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: Optional[ListNode], l2: Optional[ListNode]) -> Optional[ListNode]:

        value_1 = 0

        value_2 = 0

        num = 1

        while l1:

            value_1 += num * l1.val

            l1 = l1.next

            num *= 10  

        num = 1

        while l2:

            value_2 += num * l2.val

            l2 = l2.next

            num *= 10

        ANS = value_1 + value_2

        header = None

        linked_list = None

        for c in str(ANS): # convert ans to string and append in reverse order

            if not header:

                header = ListNode(int(c))

                linked_list = header

            else:

                node = ListNode(int(c),linked_list)

                linked_list = node

        return linked_list

https://leetcode.com/problems/add-two-numbers/description/?envType=featured-list&envId=top-interview-questions?envType=featured-list&envId=top-interview-questions