// ****************************

using System;

using System.Collections.Generic;

​

public class Person {

    public string Name { get; set; }

    public Person Father { get; set; }

    public Person Mother { get; set; }

​

    public Person(string name, Person father, Person mother) {

        Name = name;

        Father = father;

        Mother = mother;

    }

}

​

​

public class Test

{

  public static void Main()

  {

    var pebbles

        = new Person("Pebbles",

            new Person("F",

                new Person("FF",

                    new Person("FFF",

                        new Person("FFFF", null, null),

                        null),

                    null),

                new Person("FM", null, null)

            ),

            new Person("M",

                new Person("MF",

                    new Person("MFF", null, null),

                    new Person("MFM", 

                        new Person("MFMF", null, null),

                        new Person("MFMM", null, null)

                    )

                ),

                new Person("MM", null, null)

            )

        );

​

    var names = getNamesOfAllAncestors(pebbles);

    Console.WriteLine("unbound result: {0}", string.Join(", ", names));

    for (int i=0; i<=5; i++) {

        names = getNamesOfAllAncestors(pebbles, i);

        Console.WriteLine("result bound to {0} level{1} of ancestry: {2}", i, ((i==1) ? "" : "s"), string.Join(", ", names));

    }

  }

  static List<string> getNamesOfAllAncestors(Person p, int? maxRecurseLevel=null, List<string> resultList = null) {

    if (resultList == null)

        resultList = new List<string>();

​

    if ((maxRecurseLevel == null) || (maxRecurseLevel.Value > 0)) {

        if (p.Name != null)

            resultList.Add(p.Name);

        if (maxRecurseLevel != null) {

            --maxRecurseLevel;

        }

        if (p.Mother != null)

            getNamesOfAllAncestors(p.Mother, maxRecurseLevel, resultList);

        if (p.Father != null)

            getNamesOfAllAncestors(p.Father, maxRecurseLevel, resultList);

    }

    return resultList;

  }

}

​