public static T RandomElement <T>(this IEnumerable <T> e, DeepCloneableRandom rnd)
{
IList <T> arr = e as IList <T> ??
e.ToArray();
return(arr[rnd.Next(arr.Count)]);
}
public static Span <T> Shuffle <T>(this Span <T> list, DeepCloneableRandom rnd)
{
for (int i = 0; i < list.Length; i++)
{
int r = rnd.Next(i, list.Length);
T temp = list[i];
list[i] = list[r];
list[r] = temp;
}
return(list);
}
public static IList <T> Shuffle <T>(this IList <T> list, DeepCloneableRandom rnd)
{
for (int i = 0; i < list.Count; i++)
{
int r = rnd.Next(i, list.Count);
T temp = list[i];
list[i] = list[r];
list[r] = temp;
}
return(list);
}
// The copy constructor.
private DeepCloneableRandom(DeepCloneableRandom other)
{
_state0 = other._state0;
_state1 = other._state1;
}
//public static T Choose<T>(this IList<T> list, Random rnd) => list[rnd.Next(list.Count)]; public static T Choose <T>(this IReadOnlyList <T> list, DeepCloneableRandom rnd) => list[rnd.Next(list.Count)];
public static T[] ChooseNElements <T>(this IReadOnlyList <T> list, int amount, DeepCloneableRandom rnd)
{
int c = list.Count;
if (amount > c)
{
amount = c;
}
T[] results = new T[amount];
Span <int> indices = stackalloc int[amount];
for (int k = 0; k < amount; k++)
{
int j;
bool flag;
do
{
j = rnd.Next(c);
flag = false;
for (int i = 0; i < k; i++)
{
if (indices[i] == j)
{
flag = true;
break;
}
}
} while (flag);
results[k] = list[j];
indices[k] = j;
}
return(results);
}
