vector<Component> FindZeroIndegreeComponents(const DirectedGraph &graph) {
vector<Component> components = FindWeaklyConnectedComponents(graph);
vector<bool> top_component_flags(components.size(), true);
vector<int> vertices_components(graph.size());
for (int component_number = 0;
component_number < components.size(); ++component_number) {
for (int vertex : components[component_number]) {
vertices_components[vertex] = component_number;
}
}
for (int vertex = 0; vertex < graph.size(); ++vertex) {
for (int adj_vertex : graph.GetAdjacentVertices(vertex)) {
if (vertices_components[vertex] != vertices_components[adj_vertex]) {
top_component_flags[vertices_components[adj_vertex]] = false;
}
}
}
vector<Component> top_components;
for (int component_number = 0;
component_number < components.size(); ++component_number) {
if (top_component_flags[component_number]) {
top_components.push_back(components[component_number]);
}
}
return top_components;
}
DirectedGraph Transpose(const DirectedGraph &graph) {
DirectedGraph tr_graph = DirectedGraph(graph.size());
for (int vertex = 0; vertex < graph.size(); ++vertex) {
for (int adj_vertex : graph.GetAdjacentVertices(vertex)) {
tr_graph.AddEdge(Edge(adj_vertex, vertex));
}
}
return tr_graph;
}
void DepthFirstSearch(const DirectedGraph &graph, vector<int> &order,
vector<bool> &visited, int vertex) {
visited[vertex] = true;
for (int outgoing_vertex : graph.GetAdjacentVertices(vertex)) {
if (!visited[outgoing_vertex]) {
DepthFirstSearch(graph, order, visited, outgoing_vertex);
}
}
order.push_back(vertex);
}