### Table of Contents

### Problem

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.

Input: (2 -> 4 -> 3) + (5 -> 6 -> 4) Output: 7 -> 0 -> 8

### Solution

```
# Definition for singly-linked list.
# class ListNode:
# def __init__(self, x):
# self.val = x
# self.next = None
class Solution:
def addTwoNumbers(self, l1, l2):
"""
:type l1: ListNode
:type l2: ListNode
:rtype: ListNode
"""
carry = 0
dummy_head = pointer = ListNode(0)
while l1 or l2 or carry:
x = y = 0
if l1:
x = l1.val
l1 = l1.next
if l2:
y = l2.val
l2 = l2.next
pointer.next = ListNode((x + y + carry) % 10)
carry = (x + y + carry) // 10
pointer = pointer.next
return dummy_head.next
```

### Analysis

TC: $O(n)$