private void BuildGraph(List<String[]> lines)
{
idToVertex = new Dictionary<int, Vertex>();
allEdges = new List<Edge>();
foreach (String[] parts in lines)
{
Vertex vertex = new Vertex();
vertex.ID = int.Parse(parts[0]);
vertex.StringID = vertex.ID.ToString();
idToVertex.Add(vertex.ID, vertex);
for (int i = 1; i < parts.Length; i++)
{
int number = int.Parse(parts[i]);
if (number > vertex.ID)
{ // NOTE: Assumption: all numbers are distinct
Edge edge = new Edge();
edge.ID1 = vertex.ID;
edge.ID2 = number;
edge.End1 = vertex;
allEdges.Add(edge);
vertex.Edges.Add(edge);
}
else
{
// ignore the numbers smaller than the given vertex
}
}
}
// Some edges are missing a reference to an end because at the time the edge was created, that vertex still did not exist
foreach (Edge edge in allEdges)
{
Vertex vertex;
if (edge.End1 == null)
{
vertex = idToVertex[edge.ID1];
edge.End1 = vertex;
vertex.Edges.Add(edge);
}
else if (edge.End2 == null)
{
vertex = idToVertex[edge.ID2];
edge.End2 = vertex;
vertex.Edges.Add(edge);
}
}
//PrintAdjacencyList();
}
// Deletes the edge in question from the vertex's edge list
// Repoints the other edges to the newly created vertex
// If both of the edge's endpoints point to the same vertex (have the same id), delete such an edge
private void RearrangeEdges(Vertex vertex, Edge edge, Vertex newVertex)
{
//Console.WriteLine(String.Format("vertex {0}: {1}", vertex.ID, vertex.StringID));
for (int i = vertex.Edges.Count - 1; i >= 0; i--)
{
Edge vertexEdge = vertex.Edges[i];
//Console.WriteLine("checking edge: {0},{1}", vertexEdge.ID1, vertexEdge.ID2);
if (vertexEdge == edge)
{
//Console.WriteLine("\tremoving this edge as part of this round");
vertex.Edges.Remove(vertexEdge);
continue;
}
if (vertexEdge.End1 == vertex)
{
vertexEdge.End1 = newVertex;
vertexEdge.ID1 = newVertex.ID;
}
else if (vertexEdge.End2 == vertex)
{
vertexEdge.End2 = newVertex;
vertexEdge.ID2 = newVertex.ID;
}
//Console.WriteLine("edge became: {0},{1}", vertexEdge.ID1, vertexEdge.ID2);
}
}
private void RemoveLoops(Vertex vertex)
{
//Console.WriteLine("removing loops");
//Console.WriteLine(String.Format("vertex {0}: {1}", vertex.ID, vertex.StringID));
for (int i = vertex.Edges.Count - 1; i >= 0; i--)
{
Edge vertexEdge = vertex.Edges[i];
if (vertexEdge.ID1 == vertexEdge.ID2)
{
//Console.WriteLine("REMOVING edge: {0},{1}", vertexEdge.ID1, vertexEdge.ID2);
vertex.Edges.Remove(vertexEdge);
allEdges.Remove(vertexEdge);
}
}
}
private int DoRandomContraction()
{
Random random = new Random(DateTime.Now.Millisecond);
while (idToVertex.Count > 2)
{
int nextIndex = random.Next(0, allEdges.Count);
Edge edge = allEdges[nextIndex];
allEdges.Remove(edge);
//Console.WriteLine("removing edge {0},{1}", edge.ID1, edge.ID2);
Vertex vertex1 = edge.End1;
Vertex vertex2 = edge.End2;
idToVertex.Remove(vertex1.ID);
idToVertex.Remove(vertex2.ID);
Vertex newVertex = new Vertex();
newVertex.ID = vertex1.ID;
newVertex.StringID = String.Format("{0},{1}", vertex1.StringID, vertex2.StringID);
RearrangeEdges(vertex1, edge, newVertex);
RearrangeEdges(vertex2, edge, newVertex);
RemoveLoops(vertex1);
RemoveLoops(vertex2);
//Console.WriteLine(String.Format("vertex {0}: {1}", vertex1.ID, vertex1.StringID));
//PrintEdges(vertex1.Edges);
//Console.WriteLine(String.Format("vertex {0}: {1}", vertex2.ID, vertex2.StringID));
//PrintEdges(vertex2.Edges);
newVertex.Edges.AddRange(vertex1.Edges);
newVertex.Edges.AddRange(vertex2.Edges);
idToVertex.Add(newVertex.ID, newVertex);
//Console.WriteLine("--------------------------------------");
//PrintAdjacencyList();
}
return allEdges.Count;
//PrintAdjacencyList();
}
