Topological Sort

Topological.cs

using System;
using System.Collections.Generic;
using System.Linq;

namespace Trading.Backend.Events.Contracts.Tests
{
    public static class TopologicalTest
    {
        public static void ShouldCorrectlyOrderNodes()
        {
            //   A
            //  / \
            // B   C   F
            //  \ / \ /
            //   D   E
            var d = new Node<string>("D");
            var e = new Node<string>("E");
            var f = new Node<string>("F");
            f.Dependencies.Add(e);
            var b = new Node<string>("B");
            b.Dependencies.Add(d);
            var c = new Node<string>("C");
            c.Dependencies.Add(d);
            c.Dependencies.Add(e);
            var a = new Node<string>("A");
            a.Dependencies.Add(b);
            a.Dependencies.Add(c);

            //var list = new[] { a, b, c, d, e, f };
            var list = new[] { f, e, d, c, b, a };

            var sorted = Topological.Sort(list);

            // should output E F D C B A
            foreach(var item in sorted)
            {
                Console.WriteLine(item);
            }
        }
    }

    public static class Topological
    {
        public static IEnumerable<T> Sort<T>(IEnumerable<Node<T>> input)
        {
            var sorted = new List<Node<T>>();

            while (input.Any(x => x.Mark != NodeMark.Permanent))
            {
                var n = input.First(x => x.Mark == NodeMark.Unmarked);
                Visit(n, sorted);
            }

            return sorted.Select(x => x.Value);

            static void Visit<U>(Node<U> n, List<Node<U>> stack)
            {
                if (n.Mark == NodeMark.Permanent) return;
                if (n.Mark == NodeMark.Temp) throw new ApplicationException("Circular Dependency Detected!");

                n.Mark = NodeMark.Temp;
                foreach(var m in n.Dependencies)
                {
                    Visit(m, stack);
                }
                n.Mark = NodeMark.Permanent;
                stack.Add(n);
            }
        }
    }

    public class Node<T>
    {
        public NodeMark Mark { get; set; }
        public T Value { get; }
        public List<Node<T>> Dependencies { get; }

        public Node(T value)
        {
            Value = value;
            Mark = NodeMark.Unmarked;
            Dependencies = new List<Node<T>>();
        }
    }

    public enum NodeMark
    {
        Unmarked,
        Temp,
        Permanent
    }
}

Based on the Depth First Search from this Wikipedia article: https://en.wikipedia.org/wiki/Topological_sorting