Get all subsets of a collection

Question

I am trying to create a method that will return all subsets of a set.

For example if I have the collection 10,20,30 I will like to get the following ou

Answer 1

A simple algorithm based upon recursion:

private static List> GetPowerList(List a)
    {
        int n = a.Count;
        var sublists = new List>() { new List() };
        for (int i = 0; i < n; i++)
        {
            for (int j = i; j < n; j++)
            {
                var first = a[i];
                var last = a[j];
                if ((j - i) > 1)
                {
                    sublists.AddRange(GetPowerList(a
                        .GetRange(i + 1, j - i - 1))
                        .Select(l => l
                        .Prepend(first)
                        .Append(last).ToList()));
                }
                else sublists.Add(a.GetRange(i,j - i + 1));
            }
        }
        return sublists;
    }