List<List<string>> l = new List<List<string>>();
            l.Add(new List<string>(new string[] { "1", "5", "6", "7", "8", "9" }));//6个元素
            l.Add(new List<string>(new string[] { "1", "5", "6", "7", "8" }));//5个元素
            l.Add(new List<string>(new string[] { "5" }));
            Func<List<List<string>>, List<List<string>>, List<List<string>>> funcCombine = (source, dest) =>
                {
                    var groups = source.GroupBy(x => x.Count, x => x).OrderByDescending(x => x.Key).ToList();
                    List<List<string>> tmp = new List<List<string>>();
                    groups.Where(x => x.Key >= 10).ToList().ForEach(x => { groups.Remove(x); dest.Add(x as List<string>); });
                    for (int i = 10; i >= 5; i--)
                    {
                        foreach (var group in groups.Where(x => (x as List<string>).Count > 0))
                        {
                            var key = group.Key;
                            var sub = groups.Where(x => x.Key + key == i).SingleOrDefault();
                            if (sub != null)
                            {
                                for (int j = 0; i < Math.Min(key, sub.Key); j++)
                                {
                                    var left = group.First();
                                    var right = sub.First();
                                    var combine = new List<string>(left);
                                    combine.AddRange(right);
                                    (group as List<List<string>>).Remove(left);
                                    (sub as List<List<string>>).Remove(right);
                                    tmp.Add(combine);
                                }
                            }
                        }
                    }
                    if (tmp.Count > 0)
                    {
                        foreach (var group in groups)
                        {
                            tmp.AddRange(group);
                        }
                    }
                    else
                    {
                        foreach (var group in groups)
                        {
                            dest.AddRange(group);
                        }
                    }
                    return tmp;
                };
            var result = new List<List<string>>();
            List<List<string>> current;
            while((current = funcCombine(l, result)).Count > 0);