### Undirected Graph Size

Create a method name `size`

that receives a reference to an unweighted graph containing `Int`

values using `cs1.graphs.UnweightedGraph`

, so a `UnweightedGraph<Int>`

,
and returns the size of the graph as an `Int`

.

To complete this problem you'll need to implement graph traversal.
From a given node, you want to visit all of its neighbors *except* any nodes that you've already visited.
If you use a `Set`

to track the nodes that you've visited, then you can simply return the size of that `Set`

when
you are finished.
We've provided some starter code to get you off on the right track.

For reference, `cs1.graphs.UnweightedGraph`

is declared somewhat like this:

And `cs1.graphs.GraphNode`

is declared somewhat like this: