public void RemoveDuplicates()
{
int[] arrayWithDuplicates = { 1, 1, 2, 2, 3, 3, 4, 4, 4, 5, 5, 6, 7, 7, 7, 7, 9, 9, 9 };
Console.WriteLine(string.Concat(arrayWithDuplicates));
HashSet <int> hashedArray = arrayWithDuplicates.ToHashSet();
Console.WriteLine(string.Concat(hashedArray));
}