/// <summary>
/// constructs a sub-tree
/// </summary>
/// <param name="graph"></param>
/// <param name="visitedEdges"></param>
/// <param name="startEdge"></param>
/// <returns></returns>
private MinimumSpanningTree <T> ConstructSubTree(FeatureGraph <T> graph,
HashSet <int> visitedEdges,
Edge <T> startEdge)
{
// Manages the tree being constructed.
var tree = new MinimumSpanningTree <T>();
// Manages the list of candidate edges
var tempEdges = new UniqueEdgeList <T>();
// Seed of the breadth first search (BFS)
tempEdges.AddEdge(startEdge);
// Start BFS
while (tempEdges.Count > 0)
{
// Sort the edges based on distace.
tempEdges.Sort();
Edge <T> shortestEdge = null;
var edgesToRemove = new List <Edge <T> >();
// Find the shortest edge...
foreach (var edge in tempEdges.Edges)
{
var edgeSeen = tree.HasEdgeBeenSeen(edge);
var vertexSeen = tree.HasEdgeVerticesBeenSeen(edge);
// Make sure that we havent seen this edge.
if (edgeSeen)
{
continue;
}
if (vertexSeen)
{
visitedEdges.Add(edge.ID);
edgesToRemove.Add(edge);
continue;
}
shortestEdge = edge;
tree.AddEdge(shortestEdge);
break;
}
// Remove any edges that have been used up..
edgesToRemove.ForEach(x => tempEdges.RemoveEdge(x));
edgesToRemove.ForEach(x => graph.RemoveEdge(x));
// We didnt find an edge, so we have nothing else to connect...
if (shortestEdge == null)
{
// Make sure that we assert that there are no edges left...should be the case here!
System.Diagnostics.Debug.Assert(tempEdges.Count == 0);
break;
}
visitedEdges.Add(shortestEdge.ID);
// Removes the shortest edge from the graph...
graph.RemoveEdge(shortestEdge);
var adjacentEdges = graph.GetAdjacentEdgesFromEdgeVertices(shortestEdge);
//adjacentEdges.Sort();
tempEdges.AddEdges(adjacentEdges.Edges);
// Remove the shortest edge from the list of available edges left...
tempEdges.RemoveEdge(shortestEdge);
}
return(tree);
}
