Day 5-1

day5.erl

@@ -0,0 +1,49 @@
+-module(day5).
+
+-compile(export_all).
+-export([solve/1]).
+
+
+solve(InputData) ->
+	[DiagramData, Instructions] = binary:split(InputData, <<"\n\n">>, [trim_all]),
+	Diagram = lists:reverse(binary:split(DiagramData, <<"\n">>, [trim_all, global])),
+	Stacks = parse_diagram(Diagram),
+	EndStacks = eval_instructions(Instructions, Stacks),
+	{print_stacks(EndStacks), none}.
+
+print_stacks(Stacks) ->
+	lists:reverse(
+	  maps:fold(fun (_Key, [Top|_Rest], Acc) -> [Top|Acc] end, [], Stacks)
+	 ).
+
+eval_instructions(<<>>, Stacks) -> Stacks;
+eval_instructions(Instructions, Stacks) ->
+	<<"move ", Instruction1/binary>> = Instructions,
+	{Moves, Instruction2} = parse_int(Instruction1),
+	<<" from ", DigitFrom, " to ", DigitTo, $\n, Rest/binary>> = Instruction2,
+	eval_instructions(Rest, eval_move(DigitFrom, DigitTo, Moves, Stacks)).
+	
+parse_int(String) -> parse_int(String, 0).
+parse_int(<<Char, Rest/binary>>, Acc) when Char >= $0 andalso Char =< $9 -> parse_int(Rest, Acc*10+(Char - $0));
+parse_int(String, Acc) -> {Acc, String}.
+
+eval_move(_DigitFrom, _DigitTo, 0, Stacks) -> Stacks;
+eval_move(DigitFrom, DigitTo, N, Stacks) when is_integer(N) and (N > 0) ->
+	#{DigitFrom := [Item | StackFrom], DigitTo := StackTo} = Stacks,
+	eval_move(DigitFrom, DigitTo, N-1, Stacks#{DigitFrom := StackFrom, DigitTo := [Item | StackTo]}).
+
+parse_diagram([Program | Boxes]) -> parse_diagram(Program, Boxes, #{}).
+
+parse_diagram(<<>>, _Boxes, Stacks) -> Stacks;
+parse_diagram(<<Digit, ProgramRest/binary>>, Boxes, Stacks) when Digit >= $0 andalso Digit =< $9 ->
+	parse_diagram(
+	  ProgramRest,
+	  lists:map(fun(<<_, Tail/binary>>) -> Tail end, Boxes),
+	  Stacks#{Digit => build_stack(Boxes, [])}
+	 );
+parse_diagram(<<_Char, ProgramRest/binary>>, Boxes, Stacks) ->
+	parse_diagram(ProgramRest, lists:map(fun(<<_, Tail/binary>>) -> Tail end, Boxes), Stacks).
+
+build_stack([], Stack) -> Stack;
+build_stack([<<$\s, _Rest/binary>> | _Rows], Stack) -> Stack;
+build_stack([<<Item, _Rest/binary>> | Rows], Stack) -> build_stack(Rows, [Item | Stack]).