main.erl

-module(main).
-export([nub/1, nub2/1, test/0]).
-import(lists, [reverse/1]).

nub(List) ->
  Reversed = nub(List, sets:new(), []),
  reverse(Reversed).

nub([], _, Result) -> Result;
nub([X|Xs], Set, Result) ->
  case sets:is_element(X, Set) of
    true -> nub(Xs, Set, Result);
    false -> nub(Xs, sets:add_element(X, Set), [X|Result])
  end.

nub2(List) ->
  nub(reverse(List), sets:new(), []).

test() ->
  [2,4,1,3] = nub([2,4,1,3,3,1]),
  [2,4,3,1] = nub2([2,4,1,3,3,1]),
  ok.