public static IReadOnlyList <Cycle <TVertex> > GetCycles <TVertex, TEdge>(
this BidirectionalGraph <TVertex, TEdge> graph)
where TEdge : IEdge <TVertex>
{
// Initialize vertex, and current stack tracking
var visited = new HashSet <TVertex>();
var stack = new List <TVertex>();
var cycles = new List <Cycle <TVertex> >();
// Call the recursive helper function to detect cycle in different DFS trees
foreach (var vertex in graph.Vertices)
{
_logger.Debug($"Probing node '{vertex}' for cyclical dependencies...");
graph.FindCycles(vertex, visited, stack, cycles);
}
return(cycles);
}
private static void FindCycles <TVertex, TEdge>(
this BidirectionalGraph <TVertex, TEdge> executionGraph,
TVertex vertex,
HashSet <TVertex> visited,
List <TVertex> stack,
List <Cycle <TVertex> > cycles)
where TEdge : IEdge <TVertex>
{
// Do we have a circular dependency?
if (stack.Contains(vertex))
{
var cycle = new Cycle <TVertex>
{
Vertex = vertex.ToString(),
Path = stack.SkipWhile(x => !x.Equals(vertex))
.Concat(new[] { vertex })
.ToList()
};
if (_logger.IsDebugEnabled)
{
_logger.Debug($"Cycle found for vertex '{cycle.Vertex}': {string.Join(" --> ", cycle.Path.Select(x => x.ToString()))}");
}
cycles.Add(cycle);
visited.Add(vertex);
return;
}
// If we've already evaluated this vertex, stop now.
if (visited.Contains(vertex))
{
return;
}
// Mark the current node as visited and part of recursion stack
visited.Add(vertex);
stack.Add(vertex);
try
{
var children = executionGraph
.OutEdges(vertex)
.Select(x => x.Target)
.ToList();
if (_logger.IsDebugEnabled)
{
if (children.Any())
{
_logger.Debug($"Children of {vertex}: {string.Join(" => ", children.Select(x => x.ToString()))}");
}
}
foreach (var child in children)
{
executionGraph.FindCycles(child, visited, stack, cycles);
}
}
finally
{
stack.Remove(vertex);
}
}
