day10.erl

-module(day10).
-export([main/1]).
-mode(compile).

main([File]) ->
    {ok, Bin} = file:read_file(File),
    Lines = re:split(Bin, "\n", [multiline, trim, {return, list}]),
    io:format("~p~n", [run(Lines)]).

run(Lines) ->
    {P1, P2, _} = lists:foldl(fun run/2, {0,[],[]}, Lines),
    {P1, lists:nth(trunc(length(P2)/2), lists:sort(P2))}.

run([$)|T], {P1, P2, [$(|Acc]}) -> run(T, {P1, P2, Acc});
run([$]|T], {P1, P2, [$[|Acc]}) -> run(T, {P1, P2, Acc});
run([$}|T], {P1, P2, [${|Acc]}) -> run(T, {P1, P2, Acc});
run([$>|T], {P1, P2, [$<|Acc]}) -> run(T, {P1, P2, Acc});
run([$)|_], {P1, P2, _}) -> {P1+3, P2, []};
run([$]|_], {P1, P2, _}) -> {P1+57, P2, []};
run([$}|_], {P1, P2, _}) -> {P1+1197, P2, []};
run([$>|_], {P1, P2, _}) -> {P1+25137, P2, []};
run([H|T], {P1, P2, Acc}) -> run(T, {P1, P2, [H|Acc]});
run([], {P1, P2, Acc}) ->
    N = lists:foldl(fun($(,N) -> N*5+1
                    ;  ($[,N) -> N*5+2
                    ;  (${,N) -> N*5+3
                    ;  ($<,N) -> N*5+4
                    end, 0, Acc),
    {P1, [N|P2], []}.