I was trying to find an old, freely available graph theory textbook to perhaps send you to, and I found something very interesting instead. There are now a LOT of such freely available textbooks and lecture note. And they seem to be legit and not just download sites. How does anyone make a profit anymore?

Anyway, I then googled the following, and there was a lot there: "Nearest Neighbor" graph theory pdf

Hopefully you'll find something there that will help.