private static readonly Random random = new Random();
public static List<T> Shuffle(List<T> list)
{
    List<T> l = new List<T>(list);
    for (int i = l.Count - 1; i > 1; --i)
    {
        int pos = random.Next(0, i);
        T item = l[i];
        l[i] = l[pos];    // move random num to end of list.
        l[pos] = item;
    }
    return l;
}