Concatenation of Array

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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: After copying nums array into twice, it looks like this.
[nums[0],nums[1],nums[2],nums[0],nums[1],nums[2]]
[1, 2, 1, 1, 2, 1]
Example 1
Input: nums = [1,3,2,1]
Output: [1,3,2,1,1,3,2,1]

Contents

Solution - copy elements from source array to destination array with index locations

In this approach, we are going to create ans array with 2n size and then copy elements from nums array using below logic:

Java
ans[i] = nums[i];
ans[i+nums.length] = nums[i];
So, when we copy nums[i] to ans array, we copy to two target indexes, that is to ith index and to i + nums.lengthth index.

Java
import java.util.Arrays;

public class ConcatenationOfArray {

    static int[] getConcatenation(int[] nums) {
        int[] ans = new int[nums.length *2];
        for(int i=0;i<nums.length; i++) {
            ans[i] = nums[i];
            ans[i+nums.length] = nums[i];
        }
        return ans;
    }

}
Complexity Analysis:

Time complexity: Above code runs in O(n) time where n is the length of nums array, this is because we are looping through nums array.
Space complexity: O(n) since we have to return ans array with 2n size.

Above implementations source code can be found at GitHub link for Java code