public void Dijikstra_Smoke_Test()
{
var graph = new WeightedDiGraph <char, int>();
graph.AddVertex('S');
graph.AddVertex('A');
graph.AddVertex('B');
graph.AddVertex('C');
graph.AddVertex('D');
graph.AddVertex('T');
graph.AddEdge('S', 'A', 8);
graph.AddEdge('S', 'C', 10);
graph.AddEdge('A', 'B', 10);
graph.AddEdge('A', 'C', 1);
graph.AddEdge('A', 'D', 8);
graph.AddEdge('B', 'T', 4);
graph.AddEdge('C', 'D', 1);
graph.AddEdge('D', 'B', 1);
graph.AddEdge('D', 'T', 10);
var algorithm = new DijikstraShortestPath <char, int>(new DijikstraShortestPathOperators());
var result = algorithm.GetShortestPath(graph, 'S', 'T');
Assert.AreEqual(15, result.Length);
var expectedPath = new char[] { 'S', 'A', 'C', 'D', 'B', 'T' };
for (int i = 0; i < expectedPath.Length; i++)
{
Assert.AreEqual(expectedPath[i], result.Path[i]);
}
}
GetAllPairShortestPaths(WeightedDiGraph <T, W> graph)
{
var workGraph = graph.Clone();
//add an extra vertex with zero weight edge to all nodes
var randomVetex = operators.RandomVertex();
if (workGraph.Vertices.ContainsKey(randomVetex))
{
throw new Exception("Random Vertex is not unique for given graph.");
}
workGraph.AddVertex(randomVetex);
foreach (var vertex in workGraph.Vertices)
{
workGraph.AddEdge(randomVetex, vertex.Key, operators.DefaultValue);
}
//now compute shortest path from random vertex to all other vertices
var bellmanFordSP = new BellmanFordShortestPath <T, W>(operators);
var bellFordResult = new Dictionary <T, W>();
foreach (var vertex in workGraph.Vertices)
{
var result = bellmanFordSP.GetShortestPath(workGraph, randomVetex, vertex.Key);
bellFordResult.Add(vertex.Key, result.Length);
}
//adjust edges so that all edge values are now +ive
foreach (var vertex in workGraph.Vertices)
{
foreach (var edge in vertex.Value.OutEdges.ToList())
{
vertex.Value.OutEdges[edge.Key] = operators.Substract(
operators.Sum(bellFordResult[vertex.Key], edge.Value),
bellFordResult[edge.Key.Value]);
}
}
workGraph.RemoveVertex(randomVetex);
//now run dijikstra for all pairs of vertices
//trace path
var dijikstras = new DijikstraShortestPath <T, W>(operators);
var finalResult = new List <AllPairShortestPathResult <T, W> >();
foreach (var vertexA in workGraph.Vertices)
{
foreach (var vertexB in workGraph.Vertices)
{
var source = vertexA.Key;
var dest = vertexB.Key;
var sp = dijikstras.GetShortestPath(workGraph, source, dest);
//no path exists
if (sp.Length.Equals(operators.MaxValue))
{
continue;
}
var distance = sp.Length;
var path = sp.Path;
finalResult.Add(new AllPairShortestPathResult <T, W>(source, dest, distance, path));
}
}
return(finalResult);
}
