/// <summary>
/// Adds temporary edges to the graph to make all vertex even.
/// </summary>
/// <param name="edgeFactory">Edge factory method.</param>
/// <returns>Temporary edges list.</returns>
public TEdge[] AddTemporaryEdges(EdgeFactory <TVertex, TEdge> edgeFactory)
{
if (edgeFactory is null)
{
throw new ArgumentNullException(nameof(edgeFactory));
}
// First gather odd edges
List <TVertex> oddVertices = VisitedGraph.OddVertices().ToList();
// Check that there are an even number of them
if (oddVertices.Count % 2 != 0)
{
throw new InvalidOperationException("Number of odd vertices in not even.");
}
// Add temporary edges to create even edges
_temporaryEdges = new List <TEdge>();
while (oddVertices.Count > 0)
{
TVertex u = oddVertices[0];
// Find adjacent odd vertex
bool found = FindAdjacentOddVertex(u, oddVertices, edgeFactory, out bool foundAdjacent);
if (!foundAdjacent)
{
// Pick another vertex
if (oddVertices.Count < 2)
{
throw new InvalidOperationException("Eulerian trail failure.");
}
TVertex v = oddVertices[1];
// Add to temporary edges
AddTemporaryEdge(u, v, oddVertices, edgeFactory);
// Set u to null
found = true;
}
if (!found)
{
oddVertices.Remove(u);
oddVertices.Add(u);
}
}
return(_temporaryEdges.ToArray());
}