public static IEnumerable <Vertex <TVertexId> > InputsTopologicalSort <TVertexId, TVertexProperty, TEdgeProperty>(
this IDirectedGraph <TVertexId, TVertexProperty, TEdgeProperty> graph,
IComparer <TVertexId> vertexIdComparer)
{
if (graph.EdgesCount == 0)
{
return(graph.Vertices);
}
var order = new List <Vertex <TVertexId> >();
var inputDegrees = new Dictionary <Vertex <TVertexId>, int>();
Heap <Vertex <TVertexId> > vertexHeap = new Heap <Vertex <TVertexId> >(
((vertex1, vertex2) => vertexIdComparer.Compare(vertex1.Id, vertex2.Id)));
foreach (Vertex <TVertexId> vertex in graph.Vertices)
{
int degree = graph.GetInputDegree(vertex);
inputDegrees.Add(vertex, degree);
if (degree == 0)
{
vertexHeap.Push(vertex);
}
}
while (vertexHeap.Count > 0)
{
Vertex <TVertexId> vertex = vertexHeap.Pop();
order.Add(vertex);
inputDegrees.Remove(vertex);
foreach (Vertex <TVertexId> neighbour in graph.GetNeighbours(vertex))
{
--inputDegrees[neighbour];
if (inputDegrees[neighbour] == 0)
{
vertexHeap.Push(neighbour);
}
}
}
return(order.Count == graph.VerticesCount
? order
: throw new DirectedCyclicGraphException("Given graph contains a cycle"));
}