Get members of an Active Directory group recursively, i.e. including subgroups

Question

Given a group like this in Active Directory:

MainGroup
  GroupA
    User1
    User2
  GroupB
    User3
  User4

I can easily determine if Us

Answer 1

    static List ad_find_all_members(string a_sSearchRoot, string a_sGroupDN, string[] a_asPropsToLoad)
    {
        using (DirectoryEntry de = new DirectoryEntry(a_sSearchRoot))
            return ad_find_all_members(de, a_sGroupDN, a_asPropsToLoad);
    }

    static List ad_find_all_members(DirectoryEntry a_SearchRoot, string a_sGroupDN, string[] a_asPropsToLoad)
    {
        string sDN = "distinguishedName";
        string sOC = "objectClass";
        string sOC_GROUP = "group";
        string[] asPropsToLoad = a_asPropsToLoad;
        Array.Sort(asPropsToLoad);
        if (Array.BinarySearch(asPropsToLoad, sDN) < 0)
        {
            Array.Resize(ref asPropsToLoad, asPropsToLoad.Length+1);
            asPropsToLoad[asPropsToLoad.Length-1] = sDN;
        }
        if (Array.BinarySearch(asPropsToLoad, sOC) < 0)
        {
            Array.Resize(ref asPropsToLoad, asPropsToLoad.Length+1);
            asPropsToLoad[asPropsToLoad.Length-1] = sOC;
        }

        List lsr = new List();

        using (DirectorySearcher ds = new DirectorySearcher(a_SearchRoot))
        {
            ds.Filter = "(&(|(objectClass=group)(objectClass=user))(memberOf=" + a_sGroupDN + "))";
            //ds.PropertiesToLoad.Clear();
            ds.PropertiesToLoad.AddRange(asPropsToLoad);
            //ds.PageSize = 1000;
            //ds.SizeLimit = 0;
            foreach (SearchResult sr in ds.FindAll())
                lsr.Add(sr);
        }

        for(int i=0;i