public IEnumerable <TEdge> GetIncomingEdges(TVertex vertex)
{
if (!IncomingEdges.ContainsKey(vertex))
{
return(Enumerable.Empty <TEdge>());
}
return(IncomingEdges[vertex].SelectMany(v => v.Value));
}
public bool RemoveEdges(TVertex source, TVertex dest)
{
if (!OutgoingEdges.ContainsKey(source))
{
return(false);
}
if (!IncomingEdges.ContainsKey(dest))
{
return(false);
}
if (!OutgoingEdges[source].ContainsKey(dest))
{
return(false);
}
OutgoingEdges[source].Remove(dest);
IncomingEdges[dest].Remove(source);
return(true);
}
public bool RemoveEdge(TVertex source, TVertex dest, TEdge data)
{
if (!OutgoingEdges.ContainsKey(source))
{
return(false);
}
if (!IncomingEdges.ContainsKey(dest))
{
return(false);
}
if (!OutgoingEdges[source].ContainsKey(dest))
{
return(false);
}
bool foundOut = OutgoingEdges.ContainsKey(source) && OutgoingEdges[source].ContainsKey(dest) && OutgoingEdges[source][dest].Remove(data);
bool foundIn = IncomingEdges.ContainsKey(dest) && IncomingEdges[dest].ContainsKey(source) && IncomingEdges[dest][source].Remove(data);
if (foundOut && !foundIn)
{
throw new Exception("Edge found in outgoing but not incoming"); // TODO: Specialized Exception
}
if (foundIn && !foundOut)
{
throw new Exception("Edge found in incoming but not outgoing"); // TODO: Specialized Exception
}
if (OutgoingEdges.ContainsKey(source) && (!OutgoingEdges[source].ContainsKey(dest) || OutgoingEdges[source][dest].Count == 0))
{
OutgoingEdges[source].Remove(dest);
}
if (IncomingEdges.ContainsKey(dest) && (!IncomingEdges[dest].ContainsKey(source) || IncomingEdges[dest][source].Count == 0))
{
IncomingEdges[dest].Remove(source);
}
return(foundOut);
}
/// <summary>
/// Returns the nodes topologically sorted into layers. Nodes with no outgoing edges are in the first layer,
/// while nodes that only point to nodes in the first layer are in the second layer, and so on. Any node that
/// points to a node that has not been added to the graph is considered detached.
/// </summary>
/// <returns>A tuple containing a list of layers and a list of detached keys.</returns>
public (List <List <TKey> > layers, List <TKey> detached) TopologicalSort()
{
// This method could probably be optimized significantly.
// Now that I know it's called a topological sort, could use Kahn's algorithm.
// However, we'll still need to take into account detached nodes where the nodes they point
// to don't actually exist.
List <List <TKey> > layers = new List <List <TKey> > {
new List <TKey>()
};
List <TKey> detached = new List <TKey>();
foreach (var kvp in OutgoingEdges)
{
TKey key = kvp.Key;
HashSet <TKey> destinations = OutgoingEdges[key];
if (OutgoingEdges[key].Count == 0)
{
layers[0].Add(key); // If a key has no outgoing edges, it's added to the first layer
}
else if (destinations.Any(dest => !OutgoingEdges.ContainsKey(dest)))
{
detached.Add(key); // If a key has any outgoing edges that are not in the graph, it is considered detached.
}
}
HashSet <TKey> satisfiedKeys = new HashSet <TKey>(layers[0]);
HashSet <TKey> unsatisfiedKeys = new HashSet <TKey>();
while (layers[layers.Count - 1].Count > 0)
{
IEnumerable <TKey> candidates =
layers[layers.Count - 1]
.SelectMany(previous => IncomingEdges.ContainsKey(previous) ? IncomingEdges[previous] : new HashSet <TKey>())
.Where(key => OutgoingEdges.ContainsKey(key))
.Concat(unsatisfiedKeys)
.Distinct();
unsatisfiedKeys.Clear();
List <TKey> currentLevel = new List <TKey>();
foreach (TKey candidate in candidates)
{
Boolean satisfied = true;
foreach (TKey outgoing in OutgoingEdges[candidate])
{
// Check if each of the outgoing keys have been set already.
if (satisfiedKeys.Contains(outgoing))
{
continue;
}
// If not, then the candidate gets bumped up to the next level.
satisfied = false;
break;
}
if (!satisfied)
{
unsatisfiedKeys.Add(candidate);
continue;
}
currentLevel.Add(candidate);
}
layers.Add(currentLevel);
foreach (var key in currentLevel)
{
satisfiedKeys.Add(key);
}
}
layers.RemoveAt(layers.Count - 1);
detached.AddRange(unsatisfiedKeys);
return(layers, detached);
}
