Hello.

Trying to find the only element that does not appear twice I wrote the following algorithm:

list = [1, 2, 3, 1, 3, 10, 200, 10, 200] # Expected result => 2

def single_one(list) do
    list
    |> Enum.reduce(%MapSet{}, fn x, acc ->
      if MapSet.member?(acc, x) do
        MapSet.delete(acc, x)
      else
        MapSet.put(acc, x)
      end
    end)
    |> MapSet.to_list()
    |> hd()
end

I have the following questions:

1. I would like to know if in Elixir it is good practice to use if else as I did in the previous algorithm.
   I could not find a way to access the first and only element of the MapSet.
   I proceeded to convert the MapSet into a list and then its head.
2. Is there a better way to get the first element of a MapSet?

Any suggestions to improve the algorithm is welcome.

Thanks.