/// <summary>
/// Get an <see cref="IEnumerable{T}"/> with order of depth-first-search.
/// </summary>
/// <typeparam name="T">The type of vertex.</typeparam>
/// <param name="graph">The graph to enumerate.</param>
/// <param name="root">The first vertex to enumerate.</param>
/// <returns>An <see cref="IEnumerable{T}"/> with order of depth-first-search.</returns>
/// <exception cref="ArgumentNullException">When <paramref name="graph"/> is <see langword="null"/>.</exception>
/// <exception cref="KeyNotFoundException">When <paramref name="root"/> is not contained in the graph.</exception>
public static IEnumerable <T> AsDFSEnumerable <T>(this IGraph <T> graph, T root)
{
if (graph == null)
{
throw ExceptionHelper.ArgumentNull(nameof(graph));
}
if (!graph.Contains(root))
{
throw ExceptionHelper.KeyNotFound();
}
return(AsDFSEnumerableIterator(graph, root));
}
/// <summary>
/// Determines whether a vertex is in a loop of an instance of <see cref="IGraph{T}"/>.
/// </summary>
/// <typeparam name="T">The type of vertex.</typeparam>
/// <param name="graph">The graph to enumerate.</param>
/// <param name="vertex">The specified vertex.</param>
/// <returns><see langword="true"/> if the <paramref name="vertex"/> is in a loop; otherwise, <see langword="false"/>.</returns>
/// <exception cref="ArgumentNullException">When <paramref name="graph"/> is <see langword="null"/>.</exception>
/// <exception cref="KeyNotFoundException">When <paramref name="vertex"/> is not contained in the graph.</exception>
public static bool IsInLoop <T>(this IGraph <T> graph, T vertex)
{
if (graph == null)
{
throw ExceptionHelper.ArgumentNull(nameof(graph));
}
if (!graph.Contains(vertex))
{
throw ExceptionHelper.KeyNotFound();
}
Stack <T> nodes = new Stack <T>();
HashSet <T> visited = new HashSet <T>();
nodes.Push(vertex);
T last = default;
while (nodes.Count != 0)
{
T current;
do
{
if (nodes.Count == 0)
{
goto ret;
}
current = nodes.Pop();
}while (visited.Contains(current));
visited.Add(current);
if (graph.TryGetHeads(current, out var heads))
{
foreach (var child in heads)
{
if (!visited.Contains(child))
{
nodes.Push(child);
}
else if (EqualityComparer <T> .Default.Equals(vertex, child) && !EqualityComparer <T> .Default.Equals(last, child))
{
return(true);
}
}
}
last = current;
}
ret:
return(false);
}