## 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 contain a single digit. Add the two numbers and return it as a linked list.

You may assume the two numbers do not contain any leading zero, except the number 0 itself.

Example 1:

Example 2:

### Solution Explanation

The approach for solving this problem will be, to traverse through each node of the linked list, carry out a sum on every step and return the final result. We just need to know the linked list data structure and the problem will be solved really easily.

```
# Definition for singly-linked list.
# class ListNode:
# def __init__(self, val=0, next=None):
# self.val = val
# self.next = nex
class Solution:
def addTwoNumbers(self, l1: Optional[ListNode], l2: Optional[ListNode]) -> Optional[ListNode]:
dummy = ListNode()
current = dummy
carry = 0
while (l1 or l2 or carry):
n1 = l1.val if l1 else 0
n2 = l2.val if l2 else 0
s = n1 + n2 + carry
current.next = ListNode(s%10)
current = current.next
carry = s//10
l1 = l1.next if l1 else None
l2 = l2.next if l2 else None
return dummy.next
```