ai1.erl

%Stanford www.ai-class.com. Optional NLP Programming
%For test use:
%ai1:decode("Esp qtcde nzyqpcpynp zy esp ezatn zq Lcetqtntlw Tyepwwtrpynp hld spwo le Olcexzfes Nzwwprp ty estd jplc.").
%corpus test 1: http://simple.wikipedia.org/wiki/Wikipedia:List_of_1000_basic_words
%corpus test 2: http://www.wordfrequency.info/files/entriesWithoutCollocates.txt

-module(ai1). 
-export([decode/1]). 

decode(List) ->
  {Min, L} = decode(25, List),
  io:format("~nMinimal cost: ~w String: ~p~n", [Min, L]).

decode(0, _) -> {9999999999, "ERROR: set bigger initial cost"};
decode(C, List) ->
  {Minlen, MinList} = decode(C-1, List),
  L = lap(C, List),
  Llen = length(corpus(L)),
  io:fwrite("Delta: ~2w\tChars: ~w\tDecode: ~p~n", [C, Llen, L]),
  if
    Llen < Minlen ->
      {Llen, L};
    true ->
      {Minlen, MinList}
  end.

lap(D, [H|T])  -> lists:append([delta(H,D)], lap(D,T));
lap(_, []) -> [].

delta(S, true) -> S - 26;
delta(S, false) -> S;
delta(A, D) -> 
  if 
    A >= $a, A =< $z ->
      delta(A + D, (A + D) > $z);
    A >= $A, A =< $Z ->
      delta(A + D, (A + D) > $Z);
    true -> A
  end.

corpus(TList) ->
  {ok, File} = file:read_file("/tmp/corpus2"),
  Crps = lists:append([binary_to_list(File),"\n",string:to_lower(TList)]),
  Bin = zlib:gzip(Crps),
  binary_to_list(Bin).