> ## Documentation Index
> Fetch the complete documentation index at: https://leetcode-py.wisl.dev/llms.txt
> Use this file to discover all available pages before exploring further.

> ## Agent Instructions
> leetcode-py is a Python LeetCode practice environment generator with one CLI: lcpy. It is not a service or platform.
> Each problem is a directory under leetcode/ with README.md, solution.py, test_solution.py, helpers.py, and playground.ipynb. lcpy gen creates them from JSON templates bundled with the package.
> Examples are backed by tests; copy them verbatim.

# Add Two Numbers Python Solution with Tests

> Tested Python solution for LeetCode 2 with 17 pytest cases. Generate a practice environment with lcpy.

LeetCode 2, Medium. Topics: Linked List, Math, Recursion. [View on LeetCode](https://leetcode.com/problems/add-two-numbers/description/).

Generate this problem as a practice environment: tested reference solution, 17 [parametrized pytest cases](/practice/testing), and a playground notebook:

```bash theme={"theme":{"light":"github-light","dark":"github-dark"}}
lcpy gen -n 2   # by problem number
lcpy gen -s add_two_numbers   # by problem name
```

## 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 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.

### Examples

![Example 1](https://assets.leetcode.com/uploads/2020/10/02/addtwonumber1.jpg)

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

```
Input: l1 = [0], l2 = [0]
Output: [0]
```

```
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.

## Solution

Reference implementation from [solution.py on GitHub](https://github.com/wislertt/leetcode-py/blob/main/leetcode/add_two_numbers/solution.py), full suite in [test\_solution.py](https://github.com/wislertt/leetcode-py/blob/main/leetcode/add_two_numbers/test_solution.py):

```python theme={"theme":{"light":"github-light","dark":"github-dark"}}
from leetcode_py import ListNode


class Solution:
    # Time: O(max(m, n))
    # Space: O(max(m, n))
    def add_two_numbers(
        self, l1: ListNode[int] | None, l2: ListNode[int] | None
    ) -> ListNode[int] | None:
        dummy = ListNode(0)
        current = dummy
        carry = 0

        while l1 or l2 or carry:
            val1 = l1.val if l1 else 0
            val2 = l2.val if l2 else 0

            total = val1 + val2 + carry
            carry = total // 10
            current.next = ListNode(total % 10)
            current = current.next

            l1 = l1.next if l1 else None
            l2 = l2.next if l2 else None

        return dummy.next
```

## Complexity

| Time         | Space        |
| ------------ | ------------ |
| O(max(m, n)) | O(max(m, n)) |

## Tags

[Grind](/catalog/grind), [NeetCode 150](/catalog/neetcode-150), [NeetCode 250](/catalog/neetcode-250), [NeetCode All](/catalog/neetcode), [AlgoMaster 75](/catalog/algo-master-75).