HashSet UnionWith () Method Performance Issues in C #

I have many HashSetthat contain different index exceptions. I combine these hashes into one big one HashSetdepending on the input. For testing purposes, I also ported HashSetto analogues List.

• The sole purpose of HashSetand Listis to exclude indexes from random number generation.

What I do in case of List:

list2 = new List<int>();
for (int d = 0; d < list1.Count; d++)
{
  if (dicCat4[30].ContainsKey(list1[d]))
  {
    list2.AddRange(dicCat4[30][list1[d]]);
  }
}

rand = 2 * RandString.Next(0 / 2, (dicCat[30].Count) / 2);
while (list2.Contains(rand))
{
  rand = 2 * RandString.Next(0 / 2, (dicCat[30].Count) / 2);
}
// action with random

As you can see, all exceptions (indexes) are combined into one list using AddRange(). Using the method, Contains()we check whether a random number is in the list or not.

The same operation can be performed using a HashSet:

excludehash = new HashSet<int>();

for (int d = 0; d < list1.Count; d++)
{
  if (dicCat4[30].ContainsKey(list1[d]))
  {
    excludehash.UnionWith(dicCat3[30][list1[d]]);
  }
}

rand = 2 * RandString.Next(0 / 2, (dicCat[30].Count) / 2);
while (excludehash.Contains(rand))
{
  rand = 2 * RandString.Next(0 / 2, (dicCat[30].Count) / 2);
}
// action with random

in this case, instead, AddRange()I use a method UnionWith()to combine HashSetindex exceptions.

, - List !, , , HashSet . , hog - HashSet UnionWith().

: HashSet ? ( : Contains(rand) hashset, , UnionWith())

P.S. :

static Dictionary<int, Dictionary<int, HashSet<int>>> dicCat3;
static Dictionary<int, Dictionary<int, List<int>>> dicCat4;

EDIT: hardcore

int inter = list1.Count;
int cco = 0;

while (inter != cco)
{
  cco = 0;

  rand = 2 * RandString.Next(0 / 2, (dicCat[30].Count) / 2);

  for (int d = 0; d < list1.Count; d++)
  {
    if (dicCat4[30].ContainsKey(list1[d]))
    {
      if (!dicCat3[30]][list1[d]].Contains(rand))
      {
        cco++;
      }
      else
      {
        break;
      }
   }
   else
   {
     cco++;
   }
 }
}