Untitled

//remember that custom routes need to go _after_ ci's default routes, as they're executed in the order you provide them
$route['default_controller'] = "welcome";
$route['404_override'] = '';
//exception 1 to your regex here
//exception 2 to your regex here
//so on...
$route['(:any)/(:any)/(:any)'] = "$2/$3/$1";

$route['([^/]+)/([^/]+)/([^/]+)'] = "$2/$3/$1";

$route['a/([^/]+)/([^/]+)/([^/]+)'] = "$2/$3/$1";

$route['(:any)/some_controller/method/'] = "some_controller/method/$1";

function method($my_param) {
    echo 'my param is '. $my_param;
}

$route['(:num)/blog/entry/'] = "blog/view/$1";

class Blog extends CI_Controller {

    function view($id) {
         echo 'fetching blog entry no ' . $id;
    }
}

<html>
<body>
link to <?= anchor('1/blog/entry/','my first post'); ?>
link to <?= anchor('2/blog/entry/','my second post'); ?>
</body>
</html>