template<class VisitorClass>
void DFSVisit(const Graph &graph, int vertex, VisitorClass visitor, std::vector<bool> *used) {
    (*used)[vertex] = true;
    visitor.OnStartVertexVisit(vertex);
    for (auto edge: graph.GetOutcomingEdgesList(vertex)) {
        if (!(*used)[edge.to]) {
            DFSVisit(graph, edge.to, visitor, used);
        }
    }
    visitor.OnEndVertexVisit(vertex);
}


template<class VisitorClass>
void DFS(const Graph &graph, const std::vector<int> &vertice_order, VisitorClass visitor) {
    std::vector<bool> used(graph.GetNumberOfVertices());
    for (auto vertex: vertice_order) {
        if (!used[vertex]) {
            visitor.OnStartVertex(vertex);
            DFSVisit(graph, vertex, visitor, &used);
        }
    }
}


template<class VisitorClass>
void DFS(const Graph &graph, VisitorClass visitor) {
    std::vector<int> standart_order(graph.GetNumberOfVertices());
    std::iota(standart_order.begin(), standart_order.end(), 0);
    DFS(graph, standart_order, visitor);
}