/// <summary>
/// <para>
/// This implementation produces results augmented with information on SCCs within the graph.
/// </para>
/// <para>
/// To prevent traversal of an edge, the <see cref="IEdgeWeigher{V, E}"/> should
/// return a negative value as an edge weigher.
/// </para>
/// </summary>
/// <param name="graph">The graph to search.</param>
/// <param name="weigher">The weigher to use.</param>
/// <returns>The SCC search result.</returns>
public IResultBase <V, E> Search(IGraph <V, E> graph, IEdgeWeigher <V, E> weigher)
{
SccResult result = new SccResult(graph);
foreach (V vertex in graph.Vertices)
{
VertexData data = result.GetData(vertex);
if (data is null)
{
Connect(graph, vertex, weigher, result);
}
}
return(result.Build());
}
/// <summary>
/// Scans the specified graph, using recursion, and produces SCC results.
/// </summary>
/// <param name="graph">The graph to search.</param>
/// <param name="vertex">The current vertex to scan and connect.</param>
/// <param name="weigher">The optional weigher to use.</param>
/// <param name="result">The graph search result.</param>
/// <returns>Augmentation vertex data for the current vertex.</returns>
private VertexData Connect(IGraph <V, E> graph, V vertex, IEdgeWeigher <V, E> weigher, SccResult result)
{
VertexData data = result.AddData(vertex);
// Scan through all egress edges of the current vertex.
foreach (E edge in graph.GetEdgesFrom(vertex))
{
V nextVertex = edge.Dst;
// If edge is not viable, skip it.
if (weigher != null && !weigher.GetWeight(edge).IsViable)
{
continue;
}
// Attempt to get the augmentation vertex data for the next vertex.
VertexData nextData = result.GetData(nextVertex);
if (nextData is null)
{
// Next vertex has not been visited yet, so do this now.
nextData = Connect(graph, nextVertex, weigher, result);
data.LowLink = Math.Min(data.LowLink, nextData.LowLink);
}
else if (result.Visited(nextData))
{
// Next vertex has been visited, which means
// it is in the same cluster as the current vertex.
data.LowLink = Math.Min(data.LowLink, nextData.Index);
}
}
if (data.LowLink == data.Index)
{
result.AddCluster(data);
}
return(data);
}