public BellmanFordShortestPathAlgorithm(EdgeWeightedDigraph graph, Int32 vertice)
{
this._distTo = new double[graph.VerticesCount];
this._edgeTo = new Edge[graph.VerticesCount];
this._onQueue = new Boolean[graph.VerticesCount];
for (int v = 0; v < graph.VerticesCount; v++)
{
this._distTo[v] = Double.PositiveInfinity;
}
this._distTo[vertice] = 0.0;
this._queue = new AST.Queue <Int32>();
this._queue.Enqueue(vertice);
this._onQueue[vertice] = true;
while (!this._queue.IsEmpty && !this.HasNegativeCycle)
{
Int32 v = this._queue.Dequeue();
this._onQueue[v] = false;
this.Relax(graph, v);
}
}
private void Relax(EdgeWeightedDigraph graph, Int32 vertice)
{
foreach (Edge edge in graph.GetAdjacentVertices(vertice))
{
Int32 target = edge.Target;
if (this._distTo[target] > this._distTo[vertice] + edge.Weight)
{
this._distTo[target] = this._distTo[vertice] + edge.Weight;
this._edgeTo[target] = edge;
if (!this._onQueue[target])
{
this._queue.Enqueue(target);
this._onQueue[target] = true;
}
}
if (this._cost++ % graph.VerticesCount == 0)
{
this.FindNegativeCycle();
if (this.HasNegativeCycle)
{
return; // Found a negative cycle.
}
}
}
}
public EdgeWeightedCycleChecker(EdgeWeightedDigraph graph)
{
this._visited = new Boolean[graph.VerticesCount];
this._onStack = new Boolean[graph.VerticesCount];
this._edgeTo = new Edge[graph.VerticesCount];
for (int i = 0; i < graph.VerticesCount; i++)
{
if (!this._visited[i])
{
this.DFS(graph, i);
}
}
}
private void FindNegativeCycle() // by finding a cycle in predecessor graph.
{
Int32 vertice = this._edgeTo.Length;
EdgeWeightedDigraph graph = new EdgeWeightedDigraph(vertice);
for (int i = 0; i < vertice; i++)
{
if (this._edgeTo[i] != null)
{
graph.AddEdge(this._edgeTo[i]);
}
}
EdgeWeightedCycleChecker checker = EdgeWeightedCycleChecker.Create(graph);
this._cycle = checker.GetCycle();
}
private void DFS(EdgeWeightedDigraph graph, Int32 vertice)
{
this._onStack[vertice] = true;
this._visited[vertice] = true;
foreach (Edge edge in graph.GetAdjacentVertices(vertice))
{
Int32 targetVertice = edge.Target;
// Short circuit if directed cycle found.
if (this._cycle != null)
{
return;
}
// Found new vertex, so recur.
if (!this._visited[targetVertice])
{
this._edgeTo[targetVertice] = edge;
this.DFS(graph, targetVertice);
}
// trace back directed cycle
else if (this._onStack[targetVertice])
{
this._cycle = new AST.Stack <Edge>();
Edge tempEdge = edge;
while (tempEdge.Source != targetVertice)
{
this._cycle.Push(tempEdge);
tempEdge = this._edgeTo[tempEdge.Source];
}
this._cycle.Push(tempEdge);
return;
}
}
this._onStack[vertice] = false;
}
public DijkstraShortestPathAlgorithm(EdgeWeightedDigraph graph, Int32 vertice)
{
foreach (Edge edge in graph.GetEdges())
{
if (edge.Weight < 0)
{
throw new InvalidOperationException("Edge" + edge + " has negative weight.");
}
}
this._distTo = new Double[graph.VerticesCount];
this._edgeTo = new Edge[graph.VerticesCount];
for (int i = 0; i < graph.VerticesCount; i++)
{
this._distTo[i] = Double.PositiveInfinity;
}
this._distTo[vertice] = 0.0;
// Relax vertices in order of distance from vertice.
this._crossingEdgesByWeight = new IndexedMinPQ <Double>(graph.VerticesCount)
{
{ vertice, this._distTo[vertice] }
};
while (!this._crossingEdgesByWeight.IsEmpty)
{
Int32 v = this._crossingEdgesByWeight.DeleteMin();
foreach (Edge edge in graph.GetAdjacentVertices(v))
{
this.Relax(edge);
}
}
}
public static EdgeWeightedCycleChecker Create(EdgeWeightedDigraph graph)
{
return(new EdgeWeightedCycleChecker(graph));
}
