// relax vertex v and put other endpoints on queue if changed
private void Relax(EdgeWeightedDigraph G, int v)
{
//for (DirectedEdge e : G.adj(v))
foreach (DirectedEdge e in G.GetAdj(v))
{
int w = e.To();
if (distTo[w] > distTo[v] + e.GetWeight())
{
distTo[w] = distTo[v] + e.GetWeight();
edgeTo[w] = e;
if (!onQueue[w])
{
queue.Enqueue(w);
onQueue[w] = true;
}
}
if (cost++ % G.GetVertices() == 0)
{
FindNegativeCycle();
if (IsNegativeCycle())
{
return; // found a negative cycle
}
}
}
}
public DijkstraAllPairsSP(EdgeWeightedDigraph G)
{
all = new DijkstraSP[G.GetVertices()];
for (int v = 0; v < G.GetVertices(); v++)
{
all[v] = new DijkstraSP(G, v);
}
}
private Stack <DirectedEdge> cycle; // directed cycle (or null if no such cycle)
public EdgeWeightedDirectedCycle(EdgeWeightedDigraph G)
{
marked = new bool[G.GetVertices()];
onStack = new bool[G.GetVertices()];
edgeTo = new DirectedEdge[G.GetVertices()];
for (int v = 0; v < G.GetVertices(); v++)
{
if (!marked[v])
{
Dfs(G, v);
}
}
}
public CycleFinder(EdgeWeightedDigraph G)
{
marked = new bool[G.GetVertices()];
onStack = new bool[G.GetVertices()];
edgeTo = new int[G.GetVertices()];
for (int v = 0; v < G.GetVertices(); v++)
{
if (!marked[v] && cycle == null)
{
Dfs(G, v);
}
}
}
public Topological(EdgeWeightedDigraph G)
{
Pre = new Queue <int>();
Post = new Queue <int>();
ReversePost = new Stack <int>();
marked = new bool[G.GetVertices()];
for (int v = 0; v < G.GetVertices(); v++)
{
if (!marked[v])
{
Dfs(G, v);
}
}
}
private void Dfs(EdgeWeightedDigraph G, int v)
{
marked[v] = true;
Pre.Enqueue(v);
foreach (DirectedEdge e in G.GetAdj(v))
{
int w = e.To();
if (!marked[w])
{
Dfs(G, w);
}
}
Post.Enqueue(v);
ReversePost.Push(v);
}
private void FindNegativeCycle()
{
int V = edgeTo.Length;
EdgeWeightedDigraph spt = new EdgeWeightedDigraph(V);
for (int v = 0; v < V; v++)
{
if (edgeTo[v] != null)
{
spt.AddEdge(edgeTo[v]);
}
}
EdgeWeightedDirectedCycle finder = new EdgeWeightedDirectedCycle(spt);
cycle = finder.GetCycle();
}
private IEnumerable <DirectedEdge> cycle; // negative cycle (or null if no such cycle)
// by finding a cycle in predecessor graph
public BellmanFordSP(EdgeWeightedDigraph G, int s)
{
distTo = new double[G.GetVertices()];
edgeTo = new DirectedEdge[G.GetVertices()];
onQueue = new bool[G.GetVertices()];
for (int v = 0; v < G.GetVertices(); v++)
{
distTo[v] = Double.PositiveInfinity;
}
distTo[s] = 0.0;
// Bellman-Ford algorithm
queue = new Queue <int>();
queue.Enqueue(s);
onQueue[s] = true;
while (queue.Count != 0 && !IsNegativeCycle())
{
int v = queue.Dequeue();
onQueue[v] = false;
Relax(G, v);
}
}
// check that algorithm computes either the topological order or finds a directed cycle
private void Dfs(EdgeWeightedDigraph G, int v)
{
onStack[v] = true;
marked[v] = true;
foreach (DirectedEdge e in G.GetAdj(v))
{
int w = e.To();
// short circuit if directed cycle found
if (cycle != null)
{
return;
}
// found new vertex, so recur
else if (!marked[w])
{
edgeTo[w] = e;
Dfs(G, w);
}
// trace back directed cycle
else if (onStack[w])
{
cycle = new Stack <DirectedEdge>();
DirectedEdge f = e;
while (f.From() != w)
{
cycle.Push(f);
f = edgeTo[f.From()];
}
cycle.Push(f);
return;
}
}
onStack[v] = false;
}
public AcyclicSP(EdgeWeightedDigraph G, int s)
{
distTo = new double[G.GetVertices()];
edgeTo = new DirectedEdge[G.GetVertices()];
for (int v = 0; v < G.GetVertices(); v++)
{
distTo[v] = Double.PositiveInfinity;
}
distTo[s] = 0.0;
ValidateVertex(s);
Topological topological = new Topological(G);
if (!topological.IsOrder())
{
throw new ArgumentException("Digraph is not acyclic.");
}
foreach (int v in topological.ReversePost)
{
foreach (DirectedEdge e in G.GetAdj(v))
{
Relax(e);
}
}
}
static void Main(string[] args)
{
EdgeWeightedDigraph G = new EdgeWeightedDigraph("tinyEWD.txt");
DijkstraSP dijkstra = new DijkstraSP(G, 0);
if (dijkstra.HasPathTo(1))
{
Queue <DirectedEdge> path = new Queue <DirectedEdge>(dijkstra.GetPathTo(1));
foreach (DirectedEdge e in path)
{
Console.WriteLine(e.From() + " -> " + e.To());
}
}
else
{
Console.WriteLine("no path");
}
// Cycles
EdgeWeightedDigraph G1 = new EdgeWeightedDigraph("tinyEWD.txt");
EdgeWeightedDigraph G2 = new EdgeWeightedDigraph("tinyEWDAG.txt"); // Acyclic WOrGraph
CycleFinder c1 = new CycleFinder(G1);
CycleFinder c2 = new CycleFinder(G2);
if (c1.IsCycle())
{
Console.WriteLine("Cycle in tinyEWD yes");
}
else
{
Console.WriteLine("Cycle in tinyEWD no");
}
if (c2.IsCycle())
{
Console.WriteLine("Cycle in tinyEWDAG yes");
}
else
{
Console.WriteLine("Cycle in tinyEWDAG no");
}
// AcyclicSP
Console.WriteLine("Acyclic ASP");
AcyclicSP asp = new AcyclicSP(G2, 5);
int v = 2;
if (asp.IsPathTo(v))
{
Console.WriteLine("path from 5 to " + v);
Queue <DirectedEdge> path = new Queue <DirectedEdge>(asp.GetPathTo(v));
foreach (DirectedEdge e in path)
{
Console.WriteLine(e.From() + " -> " + e.To());
}
}
else
{
Console.WriteLine("no path from 5 to " + v);
}
// BellmanFord
EdgeWeightedDigraph G3 = new EdgeWeightedDigraph("tinyEWDn.txt");
BellmanFordSP b = new BellmanFordSP(G3, 0);
if (!b.IsNegativeCycle())
{
Queue <DirectedEdge> q = new Queue <DirectedEdge>(b.PathTo(7));
foreach (DirectedEdge e in q)
{
Console.WriteLine(e.From() + " - > " + e.To());
}
}
else
{
Console.WriteLine("There is negative cycle");
Queue <DirectedEdge> q = new Queue <DirectedEdge>(b.GetNegativeCycle());
foreach (DirectedEdge e in q)
{
Console.WriteLine(e.From() + " - > " + e.To());
}
}
//Console.WriteLine(G.ToString());
Console.ReadLine();
}
