Laravel Undefined offset：1

I want to add a authentication when guest try to access the home page. I get the error when I try to access the home page.

Laravel Version : Laravel 5

The routes.php error version:

Route::get('auth/login', 'Auth\AuthController@getLogin');  
Route::post('auth/login', 'Auth\AuthController@postLogin');  
Route::get('auth/logout', 'Auth\AuthController@getLogout');
Route::get('auth/register', 'Auth\AuthController@getRegister'); 
Route::post('auth/register', 'Auth\AuthController@postRegister'); 
Route::get('/', ['middleware' => 'auth', function()
{
    Route::get('/', 'HomeController@index'); 
    Route::get('pages/{id}', 'PagesController@show');  
    Route::post('comment/store', 'CommentsController@store'); 
}]);

Route::group(['prefix' => 'admin', 'namespace' => 'Admin', 'middleware' =>     'auth'], function()  
{
  Route::get('/', 'AdminHomeController@index');
  Route::resource('pages', 'PagesController');
  Route::resource('comments', 'CommentsController');
});

Error Log

at HandleExceptions->handleError('8', 'Undefined offset: 1',   'G:\wamp\www\Laravel5\vendor\compiled.php', '7377', array('request' => object(Request), 'this' => object(Route))) in compiled.php line 7377

The correct origional version

Route::get('/', 'HomeController@index');  
Route::get('pages/{id}', 'PagesController@show');  
Route::post('comment/store', 'CommentsController@store'); 
Route::get('auth/login', 'Auth\AuthController@getLogin');  
Route::post('auth/login', 'Auth\AuthController@postLogin');  
Route::get('auth/logout', 'Auth\AuthController@getLogout');
Route::get('auth/register', 'Auth\AuthController@getRegister'); 
Route::post('auth/register', 'Auth\AuthController@postRegister'); 
Route::group(['prefix' => 'admin', 'namespace' => 'Admin', 'middleware' =>  'auth'], function()  
{
  Route::get('/', 'AdminHomeController@index');
  Route::resource('pages', 'PagesController');
  Route::resource('comments', 'CommentsController');
});

Update: I know solve the problem but don't know why? You can see the last four lines I declared a route group with authentication. And when I test that part, I had logged in. Now I log out the /admin prefix and I can see the login page when I try to access the root url.

So my idea is write a guestAuth middleware for users and a adminAuth middleware to administrators. Do you have better ideas?

Try with -

Route::group(['middleware' => 'auth'], function()
{
    Route::get('/', 'HomeController@index'); 
    Route::get('pages/{id}', 'PagesController@show');  
    Route::post('comment/store', 'CommentsController@store'); 
});

Check here

Is it this line of code?

Route::get('/', ['middleware' => 'auth', function()
{
    Route::get('/', 'HomeController@index'); 
    Route::get('pages/{id}', 'PagesController@show');  
    Route::post('comment/store', 'CommentsController@store'); 
}]);

Should it be?

Route::get('/', ['middleware' => 'auth'], function()
    {
        Route::get('/', 'HomeController@index'); 
        Route::get('pages/{id}', 'PagesController@show');  
        Route::post('comment/store', 'CommentsController@store'); 
    });