lst.erl

-module(lst).
-export([
    take/2,
    reverse/1, 
    palindrome/1, 
    remove/2,
    nub/1
]).

%%
%% take(N, L) -> return the N first elements of the list L
%%
take(0, _L) -> [];
take(_N, []) -> [];
take(N, [X|Xs]) when N > 0 ->
    [X | take(N-1, Xs)].

%%
%% reverse
%%
reverse([]) -> [];
reverse([X|Xs]) -> reverse(Xs) ++ [X].

%%
%% palindrome
%%
palindrome(X) -> X =:= reverse(X).

%%
%% remove(I,L) -> remove all occurrencies of X in L.
%%
remove(_X, []) -> [];
remove(X, [X|Xs]) -> remove(X,Xs);
remove(X, [Y|Xs]) -> [Y | remove(X,Xs)].

%%
%% nub(L)
%%
nub([]) -> [];
nub([X|Xs]) -> [X|nub(remove(X,Xs))].