/// <summary>
/// Determines whether the edge-weighted digraph <tt>G</tt> has a topological
/// order and, if so, finds such an order.
/// </summary>
/// <param name="g">g the edge-weighted digraph</param>
public Topological(EdgeWeightedDigraph g)
{
var finder = new EdgeWeightedDirectedCycle(g);
if (!finder.HasCycle())
{
var dfs = new DepthFirstOrder(g);
_order = dfs.ReversePost();
}
}
/// <summary>
/// Determines whether the edge-weighted digraph <tt>G</tt> has a topological
/// order and, if so, finds such an order.
/// </summary>
/// <param name="g">g the edge-weighted digraph</param>
public Topological(EdgeWeightedDigraph g)
{
var finder = new EdgeWeightedDirectedCycle(g);
if (!finder.HasCycle())
{
var dfs = new DepthFirstOrder(g);
_order = dfs.ReversePost();
}
}
public void Run()
{
// create random DAG with V vertices and E edges; then add F random edges
const int vv = 50;
const int e = 100;
const int f = 20;
var digraph = new EdgeWeightedDigraph(vv);
var vertices = new int[vv];
for (var i = 0; i < vv; i++)
vertices[i] = i;
StdRandom.Shuffle(vertices);
for (var i = 0; i < e; i++)
{
int v, w;
do
{
v = StdRandom.Uniform(vv);
w = StdRandom.Uniform(vv);
} while (v >= w);
var weight = StdRandom.Uniform();
digraph.AddEdge(new DirectedEdge(v, w, weight));
}
// add F extra edges
for (var i = 0; i < f; i++)
{
var v = StdRandom.Uniform(vv);
var w = StdRandom.Uniform(vv);
var weight = StdRandom.Uniform(0.0, 1.0);
digraph.AddEdge(new DirectedEdge(v, w, weight));
}
Console.WriteLine(digraph);
// find a directed cycle
var finder = new EdgeWeightedDirectedCycle(digraph);
if (finder.HasCycle())
{
Console.Write("Cycle: ");
foreach (var edge in finder.Cycle())
{
Console.Write(edge + " ");
}
Console.WriteLine();
}
// or give topologial sort
else
{
Console.WriteLine("No directed cycle");
}
Console.ReadLine();
}
// by finding a cycle in predecessor graph
private void FindNegativeCycle()
{
var vv = _edgeTo.Length;
var spt = new EdgeWeightedDigraph(vv);
for (var v = 0; v < vv; v++)
{
if (_edgeTo[v] != null)
{
spt.AddEdge(_edgeTo[v]);
}
}
var finder = new EdgeWeightedDirectedCycle(spt);
_cycle = finder.Cycle();
}
/// <summary>
/// Returns a negative cycle, or <tt>null</tt> if there is no such cycle.
/// </summary>
/// <returns>a negative cycle as an iterable of edges, or <tt>null</tt> if there is no such cycle</returns>
public IEnumerable <DirectedEdge> NegativeCycle()
{
for (var v = 0; v < _distTo.Length; v++)
{
// negative cycle in v's predecessor graph
if (_distTo[v][v] < 0.0)
{
var spt = new EdgeWeightedDigraph(_edgeTo.Length);
for (var w = 0; w < _edgeTo.Length; w++)
{
if (_edgeTo[v][w] != null)
{
spt.AddEdge(_edgeTo[v][w]);
}
}
var finder = new EdgeWeightedDirectedCycle(spt);
return(finder.Cycle());
}
}
return(null);
}
/// <summary>
/// Returns a negative cycle, or <tt>null</tt> if there is no such cycle.
/// </summary>
/// <returns>a negative cycle as an iterable of edges, or <tt>null</tt> if there is no such cycle</returns>
public IEnumerable<DirectedEdge> NegativeCycle()
{
for (var v = 0; v < _distTo.Length; v++)
{
// negative cycle in v's predecessor graph
if (_distTo[v][v] < 0.0)
{
var spt = new EdgeWeightedDigraph(_edgeTo.Length);
for (var w = 0; w < _edgeTo.Length; w++)
if (_edgeTo[v][w] != null)
spt.AddEdge(_edgeTo[v][w]);
var finder = new EdgeWeightedDirectedCycle(spt);
return finder.Cycle();
}
}
return null;
}
// by finding a cycle in predecessor graph
private void FindNegativeCycle()
{
var vv = _edgeTo.Length;
var spt = new EdgeWeightedDigraph(vv);
for (var v = 0; v < vv; v++)
if (_edgeTo[v] != null)
spt.AddEdge(_edgeTo[v]);
var finder = new EdgeWeightedDirectedCycle(spt);
_cycle = finder.Cycle();
}
