题解 | #回型矩阵#

import java.util.Scanner;

// 注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();
        int[][] arr1 = new int[n][n];
        boolean flag = true;
        int u = 0;
        int d = 0;
        int l = 0;
        int r = 0;
        int num = 0;
        out:
        while (flag) {
            for (int i = u; i < n - l; i++) {
                num++;
                arr1[u][i] = num;
                if (num == n * n) {
                    flag = false;
                    break out;
                }
            }
            u++;
            for (int i = u; i < n - d; i++) {
                num++;
                arr1[i][n - d - 1] = num;
                if (num == n * n) {
                    flag = false;
                    break out;
                }
            }
            l++;
            for (int i = n - l - 1; i >= 0 + r; i--) {
                num++;
                arr1[n - d - 1][i] = num;
                if (num == n * n) {
                    flag = false;
                    break out;
                }
            }
            d++;
            for (int i = n - d - 1 ; i >= 0 + u; i--) {
                num++;
                arr1[i][r] = num;
                if (num == n * n) {
                    flag = false;
                    break out;
                }
            }
            r++;

        }
        if (!flag) {
            for (int i = 0; i < n; i++) {
                for (int j = 0; j < n; j++) {
                    System.out.print(arr1[i][j] + " ");
                }
                System.out.println("");
            }
        }
    }
}