SpanningForest

Algorithm to compute the minimal spanning forest of a directed acyclic graph that covers a particular subset of importantVertices (a "Steiner Forest"), minimizing the maximum height of the resultant trees. When multiple solutions exist with the same height, one chosen is arbitrarily. (This is much simpler than the "real" algorithm which aims to minimize the sum of edge/vertex weights)

Returns the forest as a Node structure with the top-level node containing the roots of the forest