public static void invertir(int m[][]) {
        for (int i = 0; i <= m.length / 2; i++) {
            for (int j = 0; j < m[i].length - i; j++) {
                int temp = m[i][j];
                m[i][j] = m[m.length - 1 - i][m[i].length - 1 - j];
                m[m.length - 1 - i][m[i].length - 1 - j] = temp;
            }
        }
    }