+%% to compile: erlc day3A.erl
+%% to run: erl -noshell -s day5 solve
+%%
+-module(day14).
+
+-export ([solve/0, solve/1, solve/2]).
+-export ([expand_pair/4, read_input/0]).
+-compile ([export_all]).
+
+solve() ->
+ solve(['1']),
+ solve(['2']),
+ init:stop().
+
+solve(A) ->
+ solve(A, read_input()).
+
+solve(['1'], D) ->
+ io:format("The solution to ~p puzzle1 is: ~p~n", [?MODULE, solve(1, D)]);
+solve(1, D) ->
+ solution1(D);
+solve(['2'], D) ->
+ io:format("The solution to ~p puzzle2 is: ~p~n", [?MODULE, solve(2, D)]);
+solve(2, D) ->
+ solution2(D).
+
+read_input() ->
+ {ok, IO} = file:open("input.txt", 'read'),
+ Data = read_input(IO),
+ file:close(IO),
+ Data.
+
+read_input(IO) ->
+ read_input(IO, []).
+
+read_input(IO, Input) ->
+ case read_line(IO) of
+ 'eof' -> make_map(Input);
+ Line -> read_input(IO, Input ++ [Line])
+ end.
+
+read_line(IO) ->
+ case file:read_line(IO) of
+ 'eof' -> 'eof';
+ {ok, Line} -> parse_line(Line)
+ end.
+
+parse_line(Line) ->
+ string:tokens(Line, " ->\n").
+
+make_map(Input) -> make_map(Input, maps:new()).
+
+make_map([], Map) -> Map;
+make_map([[P, [Res]]|Rest], Map) ->
+ NewMap = maps:put(P, Res, Map),
+ make_map(Rest, NewMap).
+
+solution1(PolyMap) ->
+ Ets = ets:new(polymer, [set, public, named_table]),
+ Polymer = "FNFPPNKPPHSOKFFHOFOC",
+ init_counters(Ets, PolyMap),
+ io:format("~p~n", [ets:tab2list(Ets)]),
+ Pairs = make_pairs(Polymer, []),
+ io:format("expand pairs: ~p~n",[Pairs]),
+ count_pairs(Pairs, Ets),
+ [count_elems(Pair, Ets, 1) || Pair <- Pairs],
+ loop(Ets, PolyMap, 10),
+ get_max_elm(Ets) - get_min_elm(Ets).
+
+solution2(PolyMap) ->
+ Ets = ets:new(polymer, [set, public, named_table]),
+ Polymer = "FNFPPNKPPHSOKFFHOFOC",
+ init_counters(Ets, PolyMap),
+ io:format("~p~n", [ets:tab2list(Ets)]),
+ Pairs = make_pairs(Polymer, []),
+ io:format("expand pairs: ~p~n",[Pairs]),
+ count_pairs(Pairs, Ets),
+ [count_elems(Pair, Ets, 1) || Pair <- Pairs],
+ loop(Ets, PolyMap, 40),
+ get_max_elm(Ets) - get_min_elm(Ets).
+
+get_max_elm(Ets) ->
+ Ents = ets:tab2list(Ets),
+ {V, _} = lists:max([{V,X} || {{elem, X},V} <- Ents]),
+ V.
+
+get_min_elm(Ets) ->
+ Ents = ets:tab2list(Ets),
+ {V, _} = lists:min([{V,X} || {{elem, X},V} <- Ents]),
+ V.
+
+loop(Ets, _PolyMap, 0) -> ets:tab2list(Ets);
+loop(Ets, PolyMap, Count) ->
+ Counters = get_counters(Ets),
+ [update_ets(Ets, PolyMap, Counter) || Counter <- Counters],
+ loop(Ets, PolyMap, Count - 1).
+
+init_counters(Ets, PolyMap) ->
+ maps:foreach(fun([X,Y] = Key, _Value) -> ets:insert(Ets, {{elem,X},0}), ets:insert(Ets, {{elem,Y},0}), ets:insert(Ets, {{pair, Key}, 0}) end, PolyMap).
+
+update_ets(_Ets, _PolyMap, {_Key, 0}) -> ok;
+update_ets(Ets, PolyMap, {[X,Y] = Key, Value}) ->
+ V = maps:get(Key, PolyMap),
+ count_pair([X,V],Ets, Value),
+ count_pair([V,Y],Ets, Value),
+ count_pair(Key,Ets, -1 * Value),
+ count_elem(V, Ets, Value).
+
+get_counters(Ets) ->
+ Ents = ets:tab2list(Ets),
+ [{X,V} || {{pair, X},V} <- Ents].
+
+make_pairs([_], Pairs) -> Pairs;
+make_pairs([X,Y|Rest], Pairs) -> make_pairs([Y|Rest], [[X,Y]|Pairs]).
+
+count_pairs([], _Ets) -> ok;
+count_pairs([P|Rest], Ets) ->
+ count_pair(P, Ets, 1),
+ count_pairs(Rest, Ets).
+
+count_pair(P, Ets, V) ->
+ ets:update_counter(Ets, {pair,P}, {2,V}).
+
+count_elems([X,Y], Ets, V) ->
+ count_elem(X, Ets, V),
+ count_elem(Y, Ets, V).
+
+count_elem(Elem, Ets, V) ->
+ ets:update_counter(Ets, {elem,Elem}, {2,V}).
+
+expand_pair(_P, _PolyMap, _Ets, 0) -> ok;
+expand_pair([P1,P2], PolyMap, Ets, Count) when is_list(P1), is_list(P2) ->
+ expand_pair(P1,PolyMap, Ets, Count - 1);
+expand_pair([X,Y] = P, PolyMap, Ets, Count) ->
+ [V] = maps:get(P, PolyMap),
+ ets:update_counter(Ets, [V], {2,1}),
+ [expand_pair(Pa, PolyMap, Ets, Count) || Pa <- [[X,V]] ++ [[V,Y]]].
+
+
+pairs([], _PolyMap, Pairs, _Ets, 0) ->
+ Pairs;
+pairs([], PolyMap, Pairs, Ets, Count) ->
+ io:format("new pairs: ~p~n", [Pairs]),
+ pairs(Pairs, PolyMap, [], Ets, Count - 1);
+pairs([[X,Y] = P|Rest], PolyMap, Pairs, Ets, Count) ->
+ [V] = maps:get(P, PolyMap),
+ ets:update_counter(Ets, [V], {2,1}),
+ pairs(Rest, PolyMap, Pairs ++ [[X,V]] ++ [[V,Y]], Ets, Count).
+
+count(Polymer) ->
+ Ps = lists:usort(Polymer),
+ [ {count_p(P, Polymer), [P]} || P <- Ps].
+
+count_p(P, Polymer) ->
+ lists:foldl(fun(X, Acc) -> case X == P of 'true' -> Acc + 1; _ -> Acc end end, 0, Polymer).
+
+steps(Polymer, _PolyMap, 0) -> Polymer;
+steps(Polymer, PolyMap, Count) ->
+ Insert = get_insert_list(Polymer, PolyMap),
+ steps(lists:flatten(lists:zipwith(fun(A, B) -> [A,B] end, Polymer, Insert)), PolyMap, Count - 1).
+
+get_insert_list(Polymer, PolyMap) ->
+ get_insert_list(Polymer, PolyMap, []).
+
+get_insert_list([_], _PolyMap, InsertList) -> lists:reverse([[]|InsertList]);
+get_insert_list([P1,P2|Rest], PolyMap, InsertList) ->
+ V = maps:get([P1,P2], PolyMap),
+ get_insert_list([P2|Rest], PolyMap, [V|InsertList]).