Concatenation of Array

Problem

Given an integer array nums of length n, return an array ans of length 2n where for all 0 <= i < n:

• ans[i] == nums[i]
• ans[i + n] == nums[i]

In other words, ans is the concatenation of two nums arrays.

Input / Output Format

Input: Array nums of length n. Output: Array of length 2n — nums concatenated with itself.

Examples

Example 1

Input: nums = [1,2,1] → Output: [1,2,1,1,2,1]

Example 2

Input: nums = [1,3,2,1] → Output: [1,3,2,1,1,3,2,1]

Approach Hints

• Allocate ans of size 2n. Loop i = 0..n-1, set ans[i] = ans[i+n] = nums[i].
• Or simply return nums + nums / nums.concat(nums).
• Time: O(n). Space: O(n) output.