题解 | 多组_字符串_T组形式

import java.io.*;

public class Main {
    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        int t = Integer.parseInt(br.readLine());
        StringBuilder output = new StringBuilder();

        while (t-- > 0) {
            int n = Integer.parseInt(br.readLine());
            char[] chars = br.readLine().toCharArray();

            // 双指针原地交换字符
            int left = 0, right = chars.length - 1;
            while (left < right) {
                char temp = chars[left];
                chars[left++] = chars[right];
                chars[right--] = temp;
            }
            output.append(new String(chars)).append("\n");
        }
        System.out.print(output);
    }
}