Problem

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

Pre analysis

A generic destructing approach via JS language feature will solve the problem in one line. Though I will take language independent for-loop approach

Another solution

var getConcatenation = function (nums) {
  return [...nums, ...nums];
};