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# 1929. Concatenation of Array

<https://leetcode.com/problems/concatenation-of-array>

## Description

Given an integer array `nums` of length `n`, you want to create an array `ans` of length `2n` where `ans[i] == nums[i]` and `ans[i + n] == nums[i]` for `0 <= i < n` (**0-indexed**).

Specifically, `ans` is the **concatenation** of two `nums` arrays.

Return *the array* `ans`.

**Example 1:**

```
**Input:** nums = [1,2,1]
**Output:** [1,2,1,1,2,1]
**Explanation:** The array ans is formed as follows:
- ans = [nums[0],nums[1],nums[2],nums[0],nums[1],nums[2]]
- ans = [1,2,1,1,2,1]
```

**Example 2:**

```
**Input:** nums = [1,3,2,1]
**Output:** [1,3,2,1,1,3,2,1]
**Explanation:** The array ans is formed as follows:
- ans = [nums[0],nums[1],nums[2],nums[3],nums[0],nums[1],nums[2],nums[3]]
- ans = [1,3,2,1,1,3,2,1]
```

**Constraints:**

* `n == nums.length`
* `1 <= n <= 1000`
* `1 <= nums[i] <= 1000`

## ac

```java
```