A tree, where each node could have multiple parents

Question

Here's a theoretical/pedantic question: imagine properties where each one could be owned by multiple others. Furthermore, from one iteration of ownership to the next, two neighboring owners could decide to partly combine ownership. For example:

territory 1, t=0: a,b,c,d
territory 2, t=0: e,f,g,h

territory 1, t=1: a,b,g,h
territory 2, t=1: g,h

That is to say, c and d no longer own property; and g and h became fat cats, so to speak.

I'm currently representing this data structure as a tree where each child could have multiple parents. My goal is to cram this into the Composite design pattern; but I'm having issues getting a conceptual footing on how the client might go back and update previous ownership without mucking up the whole structure.

My question is twofold.

1. Easy: What is a convenient name for this data structure such that I can google it myself?

2. Hard: What am I doing wrong? When I code I try to keep the mantra, "Keep it simple, Stupid," in my head, and I feel I am breaking this credo.

Answer 1

My question is two fold: Easy: What is a convenient name for this data structure such that I can google it myself?

What you have here is not a tree, it is a graph. A multimap will help you here. But any adjacency list or adjacency matrix will give you a good start.

Here is a video on adjacency matrix and list: Youtube on adjacency matrix and list

Hard: What am I doing wrong?

This is really hard to tell. Perhaps you did not model the relationship in a proper way. It is not that hard, given a good datastructure to start with.

And, as you asked for design patterns (but you probably found out yourself), the Composite pattern will let you model such an setting with ease.