topologicalIndex

Creates a topological ordering of nodes by means of performing a depth-first search in the graph. In case an edge is encountered that creates a cycle in the graph, that edge is ignored. The ordering is returned as a map from each node to its index in the ordering.

Exploration is started from the given startingNodes. The targets function is used to find the outgoing edges of each node. startingNodes does not need to (but may) contain all nodes of the graph. targets is guaranteed to be called exactly once for each node.

The generic type T must have correct implementations of equals and hashCode, such that they consider two nodes equal if and only if they represent the same node in the graph.