URI ROUTING

[eluser]Sudz[/eluser]
hello guys,

I have url like this

www.example.com/category/show/3-fruit.
www.example.com/category/show/4-flowers.

but need to convert like this url using codeigniter routing.
www.example.com/3-fruit.

i have done something like this in config/routes.php

Code:

$route['(:num +)(-)([a-z]+)'] = "category/show/$1";

its not working what i am doing wrong. please help me.