That'd be a tough one...
Hmmm... you'd have to store a bunch of info for each node, including what stats it increased and what nodes it connected to:
*This one increases your HP by 100 and connects to nodes 2 and 3
HP_inc[1]!=100
MP_inc[1]!=0
Attack_inc[1]!=0
Defense_inc[1]!=0
Magic_inc[1]!=0
Connect_1[1]!=2
Connect_2[1]!=3
Connect_3[1]!=0
Connect_4[1]!=0
*This one increases your Attack by 1 and is at a 4-way intersection
HP_inc[2]!=0
MP_inc[2]!=0
Attack_inc[2]!=1
Defense_inc[2]!=0
Magic_inc[2]!=0
Connect_1[2]!=1
Connect_2[2]!=4
Connect_3[2]!=5
Connect_4[2]!=6
You would access the data for each node using the number of the node. For example, HP_inc[current!]!. When moving between nodes, you'd check which nodes the current one is connected to. For the graphical display, you would probably have a method that highlighted a node based on its number by checking some stored x,y positions. As for only using a node once, you'd update a variable, used[current!]!, to indicate that the upgrade is no longer available.
