working on day4

Author: analogrelay

2016/day4/day4

@@ -0,0 +1,33 @@
+#!/usr/bin/env escript
+%%! -sname day4
+
+main([]) -> main(["input.txt"]);
+main([Filename]) ->
+    compile:file("decoder.erl"),
+    Rooms = load_input(Filename),
+    io:format("Loaded ~p rooms~n", [length(Rooms)]),
+    {ok, Pid} = decoder:start_link(),
+    dispatch(Pid, Rooms),
+    ok.
+
+dispatch(_, []) -> ok;
+dispatch(Pid, [R | Rest]) ->
+    decoder:add_room(Pid, R),
+    dispatch(Pid, Rest).
+
+load_input(Filename) ->
+    {ok, File} = file:open(Filename, [read]),
+    lists:reverse(load_input(File, [])).
+
+load_input(File, List) ->
+    case file:read_line(File) of
+        {ok, Line} -> NewList = [ parse_line(Line) | List ],
+                      load_input(File, NewList);
+        eof -> List
+    end.
+
+parse_line(Line) ->
+    Tokens = string:tokens(Line, "-[]"),
+    Segments = lists:sublist(Tokens, length(Tokens) - 3),
+    [ SectorID, Checksum ] = lists:sublist(Tokens, length(Tokens) - 2, 2),
+    { Segments, SectorID, Checksum }.

2016/day4/decoder.erl

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+% Room Decoder Server
+
+-module(decoder).
+-behavior(gen_server).
+-export([start_link/0,stop/1,add_room/2]).
+-export([init/1,handle_call/3,handle_cast/2,handle_info/2,terminate/2,code_change/3]).
+
+start_link() -> gen_server:start_link(?MODULE, [], []).
+
+%% Calls
+add_room(Pid, Room) -> gen_server:cast(Pid, {add_room, Room}).
+stop(Pid) -> gen_server:call(Pid, stop).
+
+%%% Server Functions
+init([]) -> {ok, []}.
+
+handle_call(stop, _From, State) -> {stop, normal, ok, State};
+handle_call(Msg, _From, State) -> io:format("Unknown Message: ~p", [Msg]), {stop, unknown_message, State}.
+
+handle_cast({add_room, Room}, State) ->
+    % Determine if the room is a decoy
+    {ActualChecksum, IsDecoy} = check_is_decoy(Room),
+    RoomEntry = {Room, ActualChecksum, IsDecoy},
+    io:format("Adding room to DB: ~p~n", [RoomEntry]),
+
+    % Store the room in the database
+    {noreply, [ RoomEntry | State ]};
+handle_cast(Msg, State) -> io:format("Unknown Message: ~p", [Msg]), {stop, unknown_message, State}.
+
+handle_info(Msg, State) -> io:format("Unknown Message: ~p", [Msg]), {stop, unknown_message, State}.
+
+terminate(Reason, _State) -> 
+    io:format("Terminating ~p process because: ~p", ?MODULE, Reason),
+    ok.
+
+% We don't have any state migration.
+code_change(_OldVsn, State, _Extra) -> {ok, State}.
+
+%% Private
+check_is_decoy({Segments, _, Checksum}) ->
+    Letters = lists:sort(lists:flatten(Segments)),
+    Groups = lists:foldr(fun(Elem, AccIn) ->
+                    case lists:keysearch(Elem, 1, AccIn) of
+                        false ->
+                            [ {Elem, 1} | AccIn];
+                        {value, {Letter, Count}} ->
+                            lists:keyreplace(Elem, 1, AccIn, {Letter, Count + 1})
+                    end
+                end,
+                [],
+                Letters),
+    Sorted = lists:reverse(lists:keysort(2, Groups)),
+    Top5 = lists:sublist(Sorted, 1, 5),
+    ActualChecksum = [ X || {X, _} <- Top5 ],
+    {ActualChecksum, Checksum =/= ActualChecksum}.