/// <summary>
/// The Topological Sorting algorithm
/// </summary>
public static IEnumerable <T> Sort <T>(IGraph <T> Graph) where T : IComparable <T>
{
// If the graph is either null or is not a DAG, throw exception.
if (Graph == null)
{
throw new ArgumentNullException();
}
else if (!Graph.IsDirected || CyclesDetector.IsCyclic <T>(Graph))
{
throw new Exception("The graph is not a DAG.");
}
var visited = new HashSet <T>();
var topoSortStack = new DataStructures.Lists.Stack <T>();
foreach (var vertex in Graph.Vertices)
{
if (!visited.Contains(vertex))
{
_topoSortHelper <T>(Graph, vertex, ref topoSortStack, ref visited);
}
}
return(topoSortStack);
}
/// <summary>
/// Returns an enumerable collection of nodes that specify the shortest path from the source vertex to the destination vertex.
/// </summary>
public IEnumerable <TVertex> ShortestPathTo(TVertex destination)
{
if (!_nodesToIndices.ContainsKey(destination))
{
throw new Exception("Graph doesn't have the specified vertex.");
}
else if (!HasPathTo(destination))
{
return(null);
}
int dstIndex = _nodesToIndices[destination];
var stack = new DataStructures.Lists.Stack <TVertex>();
int index;
for (index = dstIndex; _distances[index] != 0; index = _predecessors[index])
{
stack.Push(_indicesToNodes[index]);
}
// Push the source vertex
stack.Push(_indicesToNodes[index]);
return(stack);
}
/// <summary>
/// Private recursive helper.
/// </summary>
private static void _topoSortHelper <T>(IGraph <T> graph, T source, ref DataStructures.Lists.Stack <T> topoSortStack, ref HashSet <T> visited) where T : IComparable <T>
{
visited.Add(source);
foreach (var adjacent in graph.Neighbours(source))
{
if (!visited.Contains(adjacent))
{
_topoSortHelper <T>(graph, adjacent, ref topoSortStack, ref visited);
}
}
topoSortStack.Push(source);
}
