#!/usr/bin/env escript

-mode(compile).

main(_) ->
    {ok, IoStream} = file:open("./input", [read_ahead]),
    Lines = parse(IoStream, []),
    io:format("Valid by old method: ~w~n", [solve_old(Lines)]),
    io:format("Valid by new method: ~w~n", [solve_new(Lines)]).

solve_old(Lines) -> solve_old(Lines, 0).

solve_old([], Acc) -> Acc;
solve_old([none|Rest], Acc) -> solve_old(Rest, Acc);
solve_old([{Min, Max, Target, Text} | Rest], Acc) ->
    Count = length(lists:filter(fun(C) -> C =:= Target end, Text)),
    Inc = if (Min =< Count) andalso (Count =< Max) -> 1;
        true -> 0
    end,
    solve_old(Rest, Acc + Inc).

solve_new(Lines) -> solve_new(Lines, 0).

solve_new([], Acc) -> Acc;
solve_new([none|Rest], Acc) -> solve_new(Rest, Acc);
solve_new([{Index1, Index2, Target, Text} | Rest], Acc) ->
    Char1 = lists:nth(Index1, Text),
    Char2 = lists:nth(Index2, Text),
    Inc = if (Char1 =:= Target) xor (Char2 =:= Target) -> 1;
        true -> 0
    end,
    solve_new(Rest, Acc + Inc).

parse(IoStream) -> parse(IoStream, []).

parse(IoStream, Acc) ->
    {Status, Terms} = io:fread(IoStream, "", "~u-~u ~c: ~s"),
    case Status of
        error -> Acc;
        ok ->
            [A, B, [Char|_], Text] = Terms,
            [{A, B, Char, Text} | parse(IoStream)]
    end.