Sharepoint - External sharing, how can I see who has what?

[five5]

Are there any Sharepoint gurus out there?

We have a couple of contractors who are allowed access to specific folders on our Sharepoint site on a project by project basis. I've searched & searched but cannot find any way of finding out which folders 'contractor-A' has access to, and which folders 'contractor-B' has access to etc.. does anyone know of such a way?

Thanks in advance