/// <summary>
/// Enumerates edges of the graph in a depth-first order starting from the single source.
/// </summary>
/// <param name="graph">The graph.</param>
/// <param name="source">The source.</param>
/// <param name="vertexCount">The number of vertices.</param>
/// <returns>An enumerator to enumerate the edges of a depth-first search tree.</returns>
/// <exception cref="ArgumentNullException">
/// <paramref name="graph"/> is <see langword="null"/>.
/// </exception>
/// <exception cref="ArgumentOutOfRangeException">
/// <paramref name="vertexCount"/> is less than zero.
/// </exception>
public IEnumerator <TEdge> EnumerateEdges(TGraph graph, int source, int vertexCount)
{
if (graph == null)
{
throw new ArgumentNullException(nameof(graph));
}
if (vertexCount < 0)
{
throw new ArgumentOutOfRangeException(nameof(vertexCount));
}
if (unchecked ((uint)source >= vertexCount))
{
yield break;
}
byte[] exploredSet = ArrayPool <byte> .Shared.Rent(vertexCount);
Array.Clear(exploredSet, 0, exploredSet.Length);
var stack = new Internal.Stack <TEdgeEnumerator>();
try
{
SetHelpers.Add(exploredSet, source);
stack.Add(graph.EnumerateOutEdges(source));
while (stack.TryTake(out TEdgeEnumerator outEdges))
{
if (!outEdges.MoveNext())
{
continue;
}
stack.Add(outEdges);
TEdge e = outEdges.Current;
if (!graph.TryGetHead(e, out int v))
{
continue;
}
if (SetHelpers.Contains(exploredSet, v))
{
continue;
}
yield return(e);
SetHelpers.Add(exploredSet, v);
stack.Add(graph.EnumerateOutEdges(v));
}
}
finally
{
stack.Dispose();
ArrayPool <byte> .Shared.Return(exploredSet);
}
}
/// <summary>
/// Enumerates vertices of the graph in a depth-first order starting from the single source.
/// </summary>
/// <param name="graph">The graph.</param>
/// <param name="source">The source.</param>
/// <param name="exploredSet">The set of explored vertices.</param>
/// <typeparam name="TExploredSet">The type of the set of explored vertices.</typeparam>
/// <returns>An enumerator to enumerate the vertices of a depth-first search tree.</returns>
/// <exception cref="ArgumentNullException">
/// <paramref name="graph"/> is <see langword="null"/>,
/// or <paramref name="exploredSet"/> is <see langword="null"/>.
/// </exception>
public IEnumerator <TVertex> EnumerateVertices <TExploredSet>(
TGraph graph, TVertex source, TExploredSet exploredSet)
where TExploredSet : ISet <TVertex>
{
if (graph == null)
{
throw new ArgumentNullException(nameof(graph));
}
if (exploredSet == null)
{
throw new ArgumentNullException(nameof(exploredSet));
}
var stack = new Internal.Stack <TEdgeEnumerator>();
try
{
exploredSet.Add(source);
yield return(source);
stack.Add(graph.EnumerateOutEdges(source));
while (stack.TryTake(out TEdgeEnumerator outEdges))
{
if (!outEdges.MoveNext())
{
continue;
}
stack.Add(outEdges);
TEdge e = outEdges.Current;
if (!graph.TryGetHead(e, out TVertex v))
{
continue;
}
if (exploredSet.Contains(v))
{
continue;
}
exploredSet.Add(v);
yield return(v);
stack.Add(graph.EnumerateOutEdges(v));
}
}
finally
{
stack.Dispose();
}
}
private static void TraverseCore <TColorMap, THandler>(TGraph graph, TVertex u, TColorMap colorMap,
THandler handler, Func <TGraph, TVertex, bool> terminationCondition)
where TColorMap : IDictionary <TVertex, Color>
where THandler : IDfsHandler <TGraph, TVertex, TEdge>
{
Debug.Assert(graph != null, "graph != null");
Debug.Assert(colorMap != null, "colorMap != null");
Debug.Assert(handler != null, "handler != null");
Debug.Assert(terminationCondition != null, "terminationCondition != null");
colorMap[u] = Color.Gray;
handler.OnDiscoverVertex(graph, u);
if (terminationCondition(graph, u))
{
colorMap[u] = Color.Black;
handler.OnFinishVertex(graph, u);
return;
}
var stack = new Internal.Stack <StackFrame <TVertex, TEdge, TEdgeEnumerator> >();
try
{
TEdgeEnumerator outEdges = graph.EnumerateOutEdges(u);
stack.Add(new StackFrame <TVertex, TEdge, TEdgeEnumerator>(u, outEdges));
while (stack.TryTake(out StackFrame <TVertex, TEdge, TEdgeEnumerator> stackFrame))
{
u = stackFrame.Vertex;
if (stackFrame.TryGetEdge(out TEdge inEdge))
{
handler.OnFinishEdge(graph, inEdge);
}
TEdgeEnumerator edges = stackFrame.EdgeEnumerator;
while (edges.MoveNext())
{
TEdge e = edges.Current;
if (!graph.TryGetHead(e, out TVertex v))
{
continue;
}
handler.OnExamineEdge(graph, e);
Color color = GetColorOrDefault(colorMap, v);
if (color == Color.None || color == Color.White)
{
handler.OnTreeEdge(graph, e);
stack.Add(new StackFrame <TVertex, TEdge, TEdgeEnumerator>(u, e, edges));
u = v;
colorMap[u] = Color.Gray;
handler.OnDiscoverVertex(graph, u);
edges = graph.EnumerateOutEdges(u);
if (terminationCondition(graph, u))
{
colorMap[u] = Color.Black;
handler.OnFinishVertex(graph, u);
return;
}
}
else
{
if (color == Color.Gray)
{
handler.OnBackEdge(graph, e);
}
else
{
handler.OnForwardOrCrossEdge(graph, e);
}
handler.OnFinishEdge(graph, e);
}
}
colorMap[u] = Color.Black;
handler.OnFinishVertex(graph, u);
}
}
finally
{
stack.Dispose();
}
}
