-module(duml).
-export([shuffle/1]).

shuffle([]) ->
    [];
shuffle([X]) ->
    [X];
shuffle(Items) ->
    N = rand:uniform(length(Items)),
    {Nth,  Rest} = inverse_nth(N, Items),
    [Nth | shuffle(Rest)].

inverse_nth(N, Items) ->
    inverse_nth([], N, Items).

inverse_nth(Stk, 1, [X | Rest]) ->
    {X, lists:reverse(Stk, Rest)};
inverse_nth(Stk, N, [X | Rest]) when N > 1 ->
    inverse_nth([X | Stk], N-1, Rest).