private static int[][] fillSquare(int[][] arr) {
        int length = arr.length,
                midpoint = (length / 2) + (length % 2),
                corner = length - 1;

        for (int i = 0; i < midpoint; i++) {
            arr[i][i] = 1;
            arr[i][corner - i] = 1;
            arr[corner - i][i] = 1;
            arr[corner - i][corner - i] = 1;
        }
        return arr;
    }