import fi.uef.cs.tra.DiGraph;
import fi.uef.cs.tra.Vertex;

import java.util.HashSet;
import java.util.Set;


public class TRAII_25_X4_skeleton implements TRAII_25_X4 {

    /**
     * SELF-EVALUATION HERE:
     *
     *
     *
     **/

    /**
     * All the vertices that do not have incoming edges.
     * @param G input graph
     * @return set of root vertices
     */
    @Override
    public Set<Vertex> rootVertics(DiGraph G) {
        Set<Vertex> roots = new HashSet<>();

        // TODO, other methods can used

        return roots;
    }

    /**
     * How many trees there are in the graph?
     * A tree has no back-, cross- or forward edges.
     * @param G input graph
     * @return number of trees
     */
    @Override
    public int treeCount(DiGraph G) {

        Set<Vertex> potentiaTreeRoots = rootVertics(G);
        // it is not obligatory to use the finding of the root,
        // but is one good starting point
        // it is anyway one obligatory part of the task X4

        // TODO here code that finds out which components are trees

        // TODO other methods can used

        return -1; // TODO
    }
}