day8/day8.erl

   1 %% to compile: erlc day8.erl
   2 %% to run: erl -noshell -s day5 solve
   3 %%
   4 -module(day8).
   5
   6 -export ([solve/0, solve/1, solve/2]).
   7 -export ([read_input/0]).
   8
   9 solve() ->
  10     solve(['1']),
  11     solve(['2']),
  12     init:stop().
  13
  14 solve(A) ->
  15     solve(A, read_input()).
  16
  17 solve(['1'], D) ->
  18     io:format("The solution to ~p puzzle1 is: ~p~n", [?MODULE, solve(1, D)]);
  19 solve(1, D) ->
  20     solution1(D);
  21 solve(['2'], D) ->
  22     io:format("The solution to ~p puzzle2 is: ~p~n", [?MODULE, solve(2, D)]);
  23 solve(2, D) ->
  24     solution2(D).
  25
  26 read_input() ->
  27     {ok, IO} = file:open("input.txt", 'read'),
  28     Data = read_input(IO),
  29     file:close(IO),
  30     Data.
  31
  32 read_input(IO) ->
  33         read_input(IO, []).
  34
  35 read_input(IO, Input) ->
  36     case read_line(IO) of
  37         'eof' ->Input;
  38         Line -> read_input(IO, lists:reverse([Line|Input]))
  39     end.
  40
  41 read_line(IO) ->
  42         case file:read_line(IO) of
  43                 'eof' -> 'eof';
  44                 {ok, Line} -> parse_line(Line)
  45         end.
  46
  47 parse_line(Line) ->
  48     [string:tokens(X, " \n") || X <- string:split(Line, "|")].
  49
  50 solution1(Input) ->
  51    lists:foldl(fun([_,X], Acc) -> count_unique(X, Acc) end, 0, Input).
  52
  53 solution2([]) -> 0;
  54 solution2([[I|[O]]|T]) ->
  55    [One] = find_length(2,I),
  56    [Seven] = find_length(3,I),
  57    [Four] = find_length(4,I),
  58    [Eight] = find_length(7,I),
  59    Three = find_three(find_length(5, I), One),
  60    Nine = find_nine(find_length(6, I), Four),
  61    [Five, Two] = find_five_and_two(find_length(5, I), Three, Four),
  62    [Six, Zero] = find_six_and_zero(find_length(6, I), Nine, One),
  63    Key = [{lists:sort(One), 1},{lists:sort(Two), 2},{lists:sort(Three), 3},{lists:sort(Four), 4},{lists:sort(Five), 5},{lists:sort(Six), 6},{lists:sort(Seven), 7},{lists:sort(Eight), 8},{lists:sort(Nine), 9}, {lists:sort(Zero), 0}],
  64    [{_, A},{_,B},{_,C},{_,D}] = [lists:keyfind(lists:sort(X), 1, Key) || X <- O],
  65    (A * 1000 + B * 100 + C * 10 + D)  + solution2(T).
  66
  67 count_unique([], V) -> V;
  68 count_unique([H|T], V) ->
  69    count_unique(T, V + count(length(H))).
  70
  71 count(2) -> 1;
  72 count(4) -> 1;
  73 count(3) -> 1;
  74 count(7) -> 1;
  75 count(_) -> 0.
  76
  77 find_length(_Len, []) -> [];
  78 find_length(Len, [H|T]) when  length(H) == Len -> [H|find_length(Len, T)];
  79 find_length(Len, [_H|T]) -> find_length(Len, T).
  80
  81 find_three([H|T], One) ->
  82    case length(minus(H, One)) of
  83            3 -> H;
  84            _ -> find_three(T, One)
  85    end.
  86
  87 find_nine([H|T], Four) ->
  88    case length(minus(H, Four)) of
  89            2 -> H;
  90            _ -> find_nine(T, Four)
  91    end.
  92
  93 find_five_and_two(Fives, Three, Four) ->
  94         N = lists:delete(Three, Fives),
  95         find_five_and_two(N, Four).
  96
  97 find_five_and_two([H,T], Four) ->
  98    case length(minus(H, Four)) of
  99            3 -> [T, H];
 100            2 -> [H, T]
 101    end.
 102 find_six_and_zero(Sixes, Nine, One) ->
 103         N = lists:delete(Nine, Sixes),
 104         find_six_and_zero(N, One).
 105
 106 find_six_and_zero([H,T], One) ->
 107    case length(minus(H, One)) of
 108            4 -> [T, H];
 109            5 -> [H, T]
 110    end.
 111
 112 minus(X, Y) ->
 113     lists:foldl(fun(T, Acc) -> lists:delete(T, Acc) end, X, Y).
 114
 115 plus(X, Y) ->
 116     lists:usort(X ++ Y).