https://www.acmicpc.net/problem/2675
.repeat을 사용해서 반복한다.
import java.util.Scanner;
public class Main {
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
int t = sc.nextInt();
for(int i = 0; i < t; i++){
int n = sc.nextInt();
String s = sc.next();
String sArr[] = s.split("");
for(int j = 0; j < sArr.length; j++){
System.out.print(sArr[j].repeat(n));
}
System.out.println();
}
sc.close();
}
}