LeetCode-in-Java

3925. Concatenate Array With Reverse

Easy

You are given an integer array nums of length n.

Construct a new array ans of length 2 * n such that the first n elements are the same as nums, and the next n elements are the elements of nums in reverse order.

Formally, for 0 <= i <= n - 1:

• ans[i] = nums[i]
• ans[i + n] = nums[n - i - 1]

Return an integer array ans.

Example 1:

Input: nums = [1,2,3]

Output: [1,2,3,3,2,1]

Explanation:

The first n elements of ans are the same as nums.

For the next n = 3 elements, each element is taken from nums in reverse order:

• ans[3] = nums[2] = 3
• ans[4] = nums[1] = 2
• ans[5] = nums[0] = 1

Thus, ans = [1, 2, 3, 3, 2, 1].

Example 2:

Input: nums = [1]

Output: [1,1]

Explanation:

The array remains the same when reversed. Thus, ans = [1, 1].

Constraints:

• 1 <= nums.length <= 100
• 1 <= nums[i] <= 100

Solution

public class Solution {
    public int[] concatWithReverse(int[] nums) {
        int n = nums.length;
        int[] ans = new int[n * 2];
        int count = 0;
        for (int i = 0; i < n; i++) {
            ans[i] = nums[i];
            count++;
        }
        for (int i = n - 1; i >= 0; i--) {
            ans[count++] = nums[i];
        }
        return ans;
    }
}

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