Required Apache,Network Administration freelancer for Need Apache expert for htaccess file rule job

I am looking for Apache expert how help me to define htacces file rules. I need htaccess file rules for redirecting URLs for one specific case.
If a user types 'example/categories' it should be redirected to 'example/public/categories'
if a user types 'example/public/categories' the URL should not be changed.

So basically the htaccess should search for '/public' after the site name or other specified string and if it does not exist then it should add '/public' after the site name.

Will need explanation so that I can edit it in the future for other cases.

Skills & Expertise Required

Apache Network Administration