题解 | #空心正方形图案#

import java.util.Scanner;
public class Main {
    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        while(scan.hasNextInt()) {
            int n = scan.nextInt();
            int x = 2 * n - 1;
            for(int i = 1; i <= n; i++) {
            
                if(i == 1 || i == n) {
                    for(int j = 1; j <= x; j++) {
                        if(j % 2 == 0) {
                            System.out.print(" ");
                        } else {
                            System.out.print("*");
                        }
                    }
                    System.out.println();
                } else if(i > 1 && i < n){
                    for(int j = 1; j <= x; j++) {
                        if(j == 1 || j == x) {
                            System.out.print("*");
                        } else {
                            System.out.print(" ");
                        }
                    }
                    System.out.println();
                }
            }
            
        }
    }
}