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lists_exercises.erl
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lists_exercises.erl
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-module(lists_exercises).
-export([reverse/1,
rmconsecutive/1,
even_fib_numbers/0,
foldl/2,
foldl/3,
rotate/2,
run_length_encode/1,
list_any/2,
anagram/2,
last_letter/1]).
% Reverse
reverse(List) ->
reverse(List, []).
reverse([], Acc) ->
Acc;
reverse([H|T], Acc) ->
reverse(T, [H|Acc]).
% Remove Consecutive
rmconsecutive([]) ->
[];
rmconsecutive([H|T]) ->
rmconsecutive(H, T).
rmconsecutive(E, []) ->
[E];
rmconsecutive(E, [E|T]) ->
rmconsecutive(E,T);
rmconsecutive(E, [H|T]) ->
[E| rmconsecutive(H,T)].
% Even Fibonacci Numbers
fib(1) ->
1;
fib(2) ->
2;
fib(N) when N > 2 ->
fib(N-1) + fib(N-2).
% list of every fibonacci number less than N.
fibs_less_than(N) when N < 1->
[];
fibs_less_than(N) ->
fibs_less_than(N, 1, []).
fibs_less_than(N, M, AccList) ->
FibM = fib(M),
case FibM < N of
true ->
fibs_less_than(N, M + 1, [ FibM | AccList]);
false ->
AccList
end.
even_fib_numbers() ->
Less_than_4mill = fibs_less_than(4000000),
Even_fibs = lists:filter(fun(X) -> X rem 2 == 0 end, Less_than_4mill),
lists:sum(Even_fibs).
% Reduce
% with accumulator
foldl(_, Acc, []) ->
Acc;
foldl(Fun, Acc, [A | T]) ->
NewAcc = Fun(A,Acc),
foldl(Fun,NewAcc,T).
% w/o accumulator
foldl(_, List) when length(List) < 2 ->
undefined;
foldl(Fun, [A, B | T]) ->
foldl(Fun, A, [B | T]).
% Rotate Lists
rotate([], _) ->
[];
rotate(L, {Dir, N}) ->
case Dir of
left ->
{Right, Left} = lists:split(N, L);
right ->
{Right, Left} = lists:split(length(L) - N, L)
end,
lists:append(Left, Right).
% Run-length encoding of a list
run_length_encode([], Acc) -> reverse(Acc);
run_length_encode([H|T], [{Count, H}|AccT]) ->
run_length_encode(T, [{Count + 1, H}|AccT]);
run_length_encode([H|T], Acc) ->
run_length_encode(T, [{1, H}] ++ Acc).
run_length_encode(L) -> run_length_encode(L, []).
% Any
list_any(F, List) ->
lists:foldl(fun(X, Y) -> F(X) or Y end, false, List).
%Anagram
anagram(List, S) ->
LowerS = string:lowercase(S),
SortedS = lists:sort(LowerS),
lists:filter(fun (X) ->
LowerH = string:lowercase(X),
LowerH =/= LowerS andalso lists:sort(LowerH) =:= SortedS
end, List).
%Last Letter game
last_letter([]) -> [];
last_letter([H|T]) -> last_letter(T, [H]).
last_letter([], Acc) ->
lists:reverse(Acc);
last_letter(List, [H|T]) ->
Letter = lists:nthtail(length(H)-1,H),
Word = find_word(Letter, List),
case Word of
[] ->
last_letter([], [H|T]);
_ ->
NewWord = [Word, H|T],
NewList = lists:delete(Word, List),
last_letter(NewList, NewWord)
end.
find_word(_L,[]) -> [];
find_word(L,[H|T]) ->
Letter = string:lowercase(L),
[A|_Rest] = string:lowercase(H),
case [A] == Letter of
true ->
H;
false ->
find_word(L,T)
end.