> ## 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.

# Sort Colors Python Solution with Tests

> Tested Python solution for LeetCode 75 with 15 pytest cases. Generate a practice environment with lcpy.

LeetCode 75, Medium. Topics: Array, Two Pointers, Sorting. [View on LeetCode](https://leetcode.com/problems/sort-colors/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 75   # by problem number
lcpy gen -s sort_colors   # by problem name
```

## Problem

Given an array `nums` with `n` objects colored red, white, or blue, sort them **in-place** so that objects of the same color are adjacent, with the colors in the order red, white, and blue.

We will use the integers `0`, `1`, and `2` to represent the color red, white, and blue, respectively.

You must solve this problem without using the library's sort function.

### Examples

```
Input: nums = [2,0,2,1,1,0]
Output: [0,0,1,1,2,2]
```

```
Input: nums = [2,0,1]
Output: [0,1,2]
```

### Constraints

* `n == nums.length`
* `1 <= n <= 300`
* `nums[i]` is either `0`, `1`, or `2`.

**Follow up:** Could you come up with a one-pass algorithm using only constant extra space?

## Solution

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

```python theme={"theme":{"light":"github-light","dark":"github-dark"}}
class Solution:
    # Dutch National Flag Algorithm - partitions array into 3 regions using 2 pointers
    # Creates: [0s][1s][2s] with left/right boundaries, mid processes unvisited elements
    # Time: O(n)
    # Space: O(1)
    def sort_colors(self, nums: list[int]) -> None:
        left = mid = 0
        right = len(nums) - 1

        while mid <= right:
            if nums[mid] == 0:
                nums[left], nums[mid] = nums[mid], nums[left]
                left += 1
                mid += 1
            elif nums[mid] == 1:
                mid += 1
            else:
                nums[mid], nums[right] = nums[right], nums[mid]
                right -= 1
```

## Complexity

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

## Tags

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