1929\. Concatenation of Array

Easy

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`