2021/day10/day10.erl

   1 %% to compile: erlc day3A.erl
   2 %% to run: erl -noshell -s day3 solve
   3 %%
   4 -module(day10).
   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, Input ++ [Line])
  39         end.
  40
  41 read_line(IO) ->
  42         case file:read_line(IO) of
  43                 'eof' -> 'eof';
  44                 {ok, Line} -> [ X || X <- Line, [X] /= "\n"]
  45         end.
  46
  47 solution1(Input) ->
  48     lists:sum([parse(X) || X <- Input]).
  49
  50 solution2(Input) ->
  51     List = [incomplete(X) || X <- Input],
  52     Filter_fail = lists:filter(fun(X) -> X /= 'failed' end, List),
  53     Scores = lists:sort([lists:foldl(fun(X, Acc) -> (Acc * 5) + value(X) end, 0, F) || F <- Filter_fail]),
  54     lists:nth(length(Scores) div 2 + 1, Scores).
  55
  56 incomplete([H|T] = Input) ->
  57     io:format("~p~n", [Input]),
  58     try
  59         incomplete(T, [partner(H)])
  60     of
  61         ok -> 'ok';
  62         {incomplete, Rest} -> Rest
  63     catch
  64         _:_ -> 'failed'
  65     end.
  66
  67 incomplete([], Expected) -> {incomplete, Expected};
  68 incomplete(Rest, []) ->  {incomplete, incomplete(Rest)};
  69
  70 incomplete([H|T], [H|Rest]) -> incomplete(T, Rest);
  71 incomplete([H|T], Expected) -> incomplete(T, [partner(H)|Expected]).
  72
  73 parse([H|T] = Input) ->
  74     io:format("~p~n", [Input]),
  75     try
  76         parse(T, [partner(H)])
  77     of
  78         _ -> 0
  79     catch
  80         _:{invalid_partner,")"} -> 3;
  81         _:{invalid_partner,"]"} -> 57;
  82         _:{invalid_partner,"}"} -> 1197;
  83         _:{invalid_partner,">"} -> 25137
  84     end.
  85
  86 parse([], Expected) -> {parsed, Expected};
  87 parse(Rest, []) ->  {incomplete, parse(Rest)};
  88
  89 parse([H|T], [H|Rest]) -> parse(T, Rest);
  90 parse([H|T], Expected) -> parse(T, [partner(H)|Expected]).
  91
  92 partner($() -> $);
  93 partner($[) -> $];
  94 partner(${) -> $};
  95 partner($<) -> $>;
  96 partner(X) -> throw({invalid_partner, [X]}).
  97
  98 value($)) -> 1;
  99 value($]) -> 2;
 100 value($}) -> 3;
 101 value($>) -> 4.