2021/day6/day6.erl

   1 %% to compile: erlc day3A.erl
   2 %% to run: erl -noshell -s day5 solve
   3 %%
   4 -module(day6).
   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_line(IO).
  34
  35 read_line(IO) ->
  36     case file:read_line(IO) of
  37         'eof' -> 'eof';
  38         {ok, Line} -> parse_line(Line)
  39     end.
  40
  41 parse_line(Line) ->
  42     Points = string:tokens(Line, " ,->\n"),
  43     parse_line([list_to_integer(X) || X <- Points], [{0,0},{1,0},{2,0},{3,0},{4,0},{5,0},{6,0},{7,0},{8,0}]).
  44
  45 parse_line([], Acc) ->
  46         io:format("input: ~p~n", [Acc]),
  47         Acc;
  48 parse_line([H|T], Acc) ->
  49     {A, V} = lists:keyfind(H, 1, Acc),
  50     parse_line(T, lists:keyreplace(H, 1, Acc, {A, V + 1})).
  51
  52 solution1(Input) ->
  53     Fish =  days(Input, 80),
  54     io:format("OUT: ~p~n", [Fish]),
  55     lists:foldl(fun({_A, V}, Acc) -> Acc + V end, 0, Fish).
  56 solution2(Input) ->
  57     Fish =  days(Input, 256),
  58     io:format("OUT: ~p~n", [Fish]),
  59     lists:foldl(fun({_A, V}, Acc) -> Acc + V end, 0, Fish).
  60 days(Input, 0) ->
  61         Input;
  62 days(Input, Count) ->
  63     New  =
  64     lists:foldl(fun({A, V}, AccIn) ->
  65         case A of
  66             0 ->
  67                 {7, V1} = lists:keyfind(7, 1, Input),
  68                 AccIn ++ [{6, V + V1},{8, V}];
  69             7 -> AccIn;
  70             _ -> AccIn ++ [{A-1, V}]
  71         end
  72         end, [], Input),
  73     days(New, Count -1).