public static void Shuffle<T>(this IList<T> list)
{
    Random rng = new Random();
    int n = list.Count;
    while (n > 1) {
        n--;
        int k = rng.Next(n + 1);
        T value = list[k];
        list[k] = list[n];
        list[n] = value;
    }
}