URL redirection and Structure problem

I am facing a problem. my website URL structure is http://www.mydomain.com/postname/category and i want it to be http://www.mydomain.com/category/postname it is easy to do from permalinks but the main problem is that there are 2600 pages it is impossible to redirect each URL you know anything that can make this task easier?

is this wordpress Then below are details
1) Login to admin --> Permalink --> Custom Structures --> paste the below code in text box --> Save changes

WordPress will automatically setup the 301's for you. Don't worry!