public IList <T> GetDirectedPath(T startPoint)
{
// we assume the graph is eularian
var(source, sink) = GetSourceAndSink();
// if source exists, sink has to exist. Or both have to be null.
// In that case we get an eularian circuit
if (source != null ^ sink != null)
{
return(null);
}
var eularianPath = new LinkedList <GraphNode <T> >();
_directedGraph.ClearEdgeColors();
// if source is null, we have an eularian circuit.
// If a start point is suggested, we use that, otherwise, we can start anywhere
if (!_directedGraph.Nodes.TryGetValue(new GraphNode <T>(startPoint), out var startNode))
{
startNode = _directedGraph.Nodes.First();
}
startNode = source ?? startNode;
while (startNode != null)
{
var partialPath = GetPartialPath(startNode);
MergePaths(eularianPath, partialPath, startNode);
startNode = GetNodeWithUnusedEdges(eularianPath);
}
return(_directedGraph.Edges.Any(x => x.Color == Color.Uncolored) ? null : eularianPath.Select(x => x.Label).ToList());
}