/// <summary>
/// Gets the incoming edges to a key, regardless if the node has been added or not.
/// </summary>
public List <TKey> GetIncoming(TKey key)
{
if (!IncomingEdges.TryGetValue(key, out HashSet <TKey> edges))
{
return(new List <TKey>());
}
return(edges.ToList());
}
private IDictionary <TVertex, IList <TEdge> > GetIncomingEdgesMap(TVertex vertex)
{
if (IncomingEdges.TryGetValue(vertex, out var map))
{
return(map);
}
map = InnerMap;
OutgoingEdges[vertex] = InnerMap;
IncomingEdges[vertex] = map;
return(map);
}
private void AddEdges(TKey key, IList <TKey> outgoing)
{
OutgoingEdges.Add(key, new HashSet <TKey>(outgoing));
foreach (var dest in outgoing)
{
if (!IncomingEdges.TryGetValue(dest, out HashSet <TKey> incoming))
{
IncomingEdges[dest] = new HashSet <TKey> {
key
}
}
;
else
{
incoming.Add(key);
}
}
}
/// <summary>
/// Checks if adding the node causes a cycle.
/// </summary>
public Boolean CausesCycle(TKey key, IList <TKey> outgoing)
{
if (outgoing.Contains(key))
{
return(true); // Self cycle
}
if (!IncomingEdges.TryGetValue(key, out HashSet <TKey> incoming) || incoming.Count == 0)
{
return(false); // No incoming edges, so we can't have a cycle.
}
// If a path exists from any outgoing edge to any incoming edge, adding the node will cause a cycle.
foreach (TKey start in outgoing)
{
foreach (TKey end in incoming)
{
if (PathExists(start, end))
{
return(true);
}
}
}
return(false);
}
public IEnumerable <TVertex> GetParents(TVertex vertex)
=> IncomingEdges.TryGetValue(vertex, out var parentMap)
? parentMap.Keys
: Enumerable.Empty <TVertex>();
