2021/day7/day7.erl

   1 %% to compile: erlc day3A.erl
   2 %% to run: erl -noshell -s day5 solve
   3 %%
   4 -module(day7).
   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     [list_to_integer(X) || X <- Points].
  44
  45 solution1(Input) ->
  46     Max = lists:max(Input),
  47     Min = lists:min(Input),
  48     io:format("Max: ~p Min: ~p~n", [Max, Min]),
  49     Fuels = [ fuel_needed(X, Input, fun fuel1/2) || X <- lists:seq(Min, Max)],
  50     lists:min(Fuels).
  51
  52 solution2(Input) ->
  53     Max = lists:max(Input),
  54     Min = lists:min(Input),
  55     io:format("Soln2: Max: ~p Min: ~p~n", [Max, Min]),
  56     Fuels = [ fuel_needed(X, Input, fun fuel2/2) || X <- lists:seq(Min, Max)],
  57     lists:min(Fuels).
  58
  59 fuel_needed(Pos, Data, Fuel_fun) ->
  60         fuel_needed(Pos, Data, Fuel_fun, 0).
  61
  62 fuel_needed(_Pos, [], _, Acc) -> Acc;
  63 fuel_needed(Pos, [H|T], Fuel_fun, Acc) ->
  64         fuel_needed(Pos, T, Fuel_fun, Acc + Fuel_fun(H, Pos)).
  65
  66 fuel1(X, X) -> 0;
  67 fuel1(X, Y) when X > Y -> X - Y;
  68 fuel1(X, Y) when Y > X -> Y - X.
  69
  70 fuel2(X, X) -> 0;
  71 fuel2(X, Y) when X > Y -> fuel_steps(X - Y);
  72 fuel2(X, Y) when Y > X -> fuel_steps(Y - X).
  73
  74 fuel_steps(X) ->
  75         fuel_steps(X, 1, 0).
  76
  77 fuel_steps(0, _Cost, Count) -> Count;
  78 fuel_steps(X, Cost, Count) ->
  79         fuel_steps(X - 1, Cost + 1, Count + Cost).