## DEV Community

### Medium

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 = , l2 = 
Output: 
```

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]
```

Constraints:

• The number of nodes in each linked list is in the range `[1, 100]`.
• `0 <= Node.val <= 9`
• It is guaranteed that the list represents a number that does not have leading zeros.

## Python Solution.

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

# Reference of head which is null at this poin
temp = None
# Carry
carry = 0
# Loop for the two lists
while l1 is not None or l2 is not None:

# At the start of each iteration, we should add carry from the last iteration
sum_value = carry
# Since the lengths of the lists may be unequal, we are checking if the
# current node is null for one of the lists
if l1 is not None:
sum_value += l1.val
l1 = l1.next
if l2 is not None:
sum_value += l2.val
l2 = l2.next
# At   this point, we will add the total sum_value % 10 to the new node
# in the resultant list
node = ListNode(sum_value % 10)
# Carry to be added in the next iteration
carry = sum_value // 10
# If this is the first node or head
if temp is None:
# for any other node
else:
temp.next = node
temp = temp.next
# After the last iteration, we will check if there is carry left
# If it's left then we will create a new node and add it
if carry > 0:
temp.next = ListNode(carry)

`````` 