/// <summary>
/// Attempts to remove an edge entering a specific vertex from the strongly connected
/// portion of a specific connected subgraph and replace it with another edge towards an
/// edge from a weakly connected portion of the connected subgraph, thus expanding the
/// strongly connected portion.
/// </summary>
/// <param name="connectedSubgraph">The connected subgraph which contains a weakly
/// connected portion.</param>
/// <param name="vertex">The vertex from the strongly connected portion of the connected
/// subgraph.</param>
/// <returns><see langword="true"/> if the edge was successfully added.</returns>
private bool AddStronglyConnectingEdgeEnteringVertex(
ConnectedSubgraph connectedSubgraph,
Vertex vertex)
{
Vertex otherVertex = null;
List<Vertex> adjacentVertices = GetAdjacentVertices(vertex);
while (adjacentVertices.Count > 0)
{
int vertexIndex = _random.Next(adjacentVertices.Count);
Vertex adjacentVertex = adjacentVertices[vertexIndex];
if (!vertex.IsConnectedToVertex(adjacentVertex)
&& connectedSubgraph.ContainsVertex(adjacentVertex)
&& !connectedSubgraph.IsVertexStronglyConnected(adjacentVertex))
{
if (connectedSubgraph.CheckWillConnectStrongly(vertex, adjacentVertex))
{
if (!CheckCanConnectVertices(vertex, adjacentVertex))
{
// If the two vertices cannot be connected without causing an
// intersection, remove the other edge
Vertex crossVertex1 = _levelMatrix[vertex.Row, adjacentVertex.Column];
Vertex crossVertex2 = _levelMatrix[adjacentVertex.Row, vertex.Column];
RemoveEdgeBetweenVertices(crossVertex1, crossVertex2);
}
// Check if the other vertex has the maximum number of edges entering it
// and if so, remove a random edge entering it
if (adjacentVertex.ConnectedVertexCount == _maxEdges)
RemoveEdgeEnteringVertex(adjacentVertex);
otherVertex = adjacentVertex;
break;
}
}
adjacentVertices.RemoveAt(vertexIndex);
}
// If no suitable other vertex was found, give up
if (otherVertex == null)
return false;
// Check if the specified vertex has the maximum number of edges entering it and if so,
// remove a random edge entering it
if (vertex.ConnectedVertexCount == _maxEdges)
RemoveEdgeEnteringVertex(vertex);
// Add the edge to the level graph
AddEdgeBetweenVertices(vertex, otherVertex);
return true;
}
