> ## 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.

# Reverse String Python Solution with Tests

> Tested Python solution for LeetCode 344 with 15 pytest cases. Generate a practice environment with lcpy.

LeetCode 344, Easy. Topics: Two Pointers, String. [View on LeetCode](https://leetcode.com/problems/reverse-string/description/).

Generate this problem as a practice environment: tested reference solution, 15 [parametrized pytest cases](/practice/testing), and a playground notebook:

```bash theme={"theme":{"light":"github-light","dark":"github-dark"}}
lcpy gen -n 344   # by problem number
lcpy gen -s reverse_string   # by problem name
```

## Problem

Write a function that reverses a string. The input string is given as an array of characters `s`.

You must do this by modifying the input array [in-place](https://en.wikipedia.org/wiki/In-place_algorithm) with `O(1)` extra memory.

### Examples

```
Input: s = ["h","e","l","l","o"]
Output: ["o","l","l","e","h"]
```

```
Input: s = ["H","a","n","n","a","h"]
Output: ["h","a","n","n","a","H"]
```

### Constraints

* 1 \<= s.length \<= 10^5
* s\[i] is a [printable ascii character](https://en.wikipedia.org/wiki/ASCII#Printable_characters).

## Solution

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

```python theme={"theme":{"light":"github-light","dark":"github-dark"}}
class Solution:
    # Time: O(n)
    # Space: O(1)
    def reverse_string(self, s: list[str]) -> None:
        left = 0
        right = len(s) - 1
        while left < right:
            s[left], s[right] = s[right], s[left]
            left += 1
            right -= 1
```

## Complexity

| Time | Space |
| ---- | ----- |
| O(n) | O(1)  |

## Tags

[NeetCode 250](/catalog/neetcode-250), [NeetCode All](/catalog/neetcode).