> ## 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.

# Remove Duplicates From Sorted Array

> Tested Python solution for LeetCode 26 with 12 pytest cases. Generate a practice environment with lcpy.

LeetCode 26, Easy. Topics: Array, Two Pointers. [View on LeetCode](https://leetcode.com/problems/remove-duplicates-from-sorted-array/description/).

Generate this problem as a practice environment: tested reference solution, 12 [parametrized pytest cases](/practice/testing), and a playground notebook:

```bash theme={"theme":{"light":"github-light","dark":"github-dark"}}
lcpy gen -n 26   # by problem number
lcpy gen -s remove_duplicates_from_sorted_array   # by problem name
```

## Problem

Given an integer array `nums` sorted in non-decreasing order, remove the duplicates **in-place** such that each unique element appears only once. The relative order of the elements should be kept the same. Then return *the number of unique elements in* `nums`.

Consider the number of unique elements of `nums` to be `k`. To get accepted, you need to do the following things:

* Change the array `nums` such that the first `k` elements of `nums` contain the unique elements in the order they were present in `nums` initially. The remaining elements of `nums` are not important as well as the size of `nums`.
* Return `k`.

### Examples

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

Explanation: Your function should return k = 2, with the first two elements of nums being 1 and 2 respectively.
It does not matter what you leave beyond the returned k (hence the underscores).
```

```
Input: nums = [0,0,1,1,1,2,2,3,3,4]
Output: 5, nums = [0,1,2,3,4,_,_,_,_,_]

Explanation: Your function should return k = 5, with the first five elements of nums being 0, 1, 2, 3, and 4 respectively.
```

### Constraints

* `1 <= nums.length <= 3 * 10^4`
* `-100 <= nums[i] <= 100`
* `nums` is sorted in non-decreasing order.

## Solution

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

```python theme={"theme":{"light":"github-light","dark":"github-dark"}}
class Solution:
    # Time: O(n)
    # Space: O(1)
    def remove_duplicates(self, nums: list[int]) -> int:
        if not nums:
            return 0
        write = 1
        for read in range(1, len(nums)):
            if nums[read] != nums[write - 1]:
                nums[write] = nums[read]
                write += 1
        return write
```

## Complexity

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

## Tags

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