There are two ways to put old Nikon lenses on Pentax.
You can turn your lens 180 degrees or so and just put it on your cameramount, but it won't de safe to hang on your camera. It will work that way. Offcourse you need lenses that have a diafragmaring to adjust the lens, since the camera has no way to communicate with the lens.
The other way is to purchase a connector that puts the Nikon mount on the K-mount. Since the flangsdistances are equal offcourse this will mean that there is glas in it. That Always means some loss in quality. The adapter turns out to be an 1.25x teleconverter, so you will have a different lens. My camera with connector to an expensive Nikonlens wich was only working with closed diafragma at f22.
I had an old Nikkorlens off 300mm/f4.5 that worked out as 375mm/f5.6 manual focus lens.
https://www.pentaxforums.com/forums/post-your-photos/104966-sports-justin-hen...-rosmalen.html
Updated it with a new link in the belowpart.
Found one, but maybe some more on internet:
http://www.amazon.com/Fotodiox-Mount-Adapter-Pentax-Camera/dp/B003EAUBDE