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# 26. Remove Duplicates from Sorted Array 🚫

**Difficulty**: `Easy` - **Tags**: `Array`, `Two Pointers`

## Description 📋

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 in `nums` to be `k`. To get accepted, you need to do the following things:

1. 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`.
2. Return `k`.

## Custom Judge 🧪

The judge will test your solution with the following code:

```python
int[] nums = [...]; // Input array
int[] expectedNums = [...]; // The expected answer with correct length

int k = removeDuplicates(nums); // Calls your implementation

assert k == expectedNums.length;
for (int i = 0; i < k; i++) {
    assert nums[i] == expectedNums[i];
}
```

If all assertions pass, then your solution will be accepted.

## Examples 🌟

**Example 1:**

**Input:**

```python
nums = [1,1,2]
```

**Output:**

```python
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 they are underscores).

**Example 2:**

**Input:**

```python
nums = [0,0,1,1,1,2,2,3,3,4]
```

**Output:**

```python
5
```

**Explanation:** Your function should return `k = 5`, with the first five elements of `nums` being 0, 1, 2, 3, and 4 respectively. It does not matter what you leave beyond the returned `k` (hence they are underscores).

## Constraints ⚙️

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

## Solution 💡

The time complexity is $O(n)$, and the space complexity is $O(1)$. Here, $n$ is the length of the array.

### Java

```java
class Solution {
    public int removeDuplicates(int[] nums) {
        if (nums.length == 0) return 0;
        int k = 1; // Start with the first unique element

        for (int i = 1; i < nums.length; i++) {
            if (nums[i] != nums[i - 1]) {
                nums[k++] = nums[i];
            }
        }

        return k;
    }
}
```

You can find the full `Solution.java` file [here](https://github.com/ChunhThanhDe/Leetcode-Top-Interview/blob/main/Topic%201%20Array%20-%20String/003%20Remove%20Duplicates%20from%20Sorted%20Array/Solution.java) and `AnotherSolution.java` file [here](https://github.com/ChunhThanhDe/Leetcode-Top-Interview/blob/main/Topic%201%20Array%20-%20String/003%20Remove%20Duplicates%20from%20Sorted%20Array/AnotherSolution.java).