Day 23-1

day23.erl

@@ -0,0 +1,151 @@
+-module(day23).
+
+-export([solve/1]).
+
+-compile(export_all).
+
+solve(InputData) ->
+    {part1(InputData), none}.
+
+part1(Input) ->
+    State = parse_input(Input),
+    EndState = step(10, State),
+    {XMin, XMax, YMin, YMax} = Bounds = get_bounds(EndState),
+    %io:format("~p~n", [Bounds]),
+    (XMax - XMin + 1) * (YMax - YMin + 1) - num_elves(State).
+
+parse_input(Input) -> parse_input(Input, 0, 0, 1, {#{}, #{}}).
+
+parse_input(<<>>, _X, _Y, _NumElves, State) ->
+    State;
+parse_input(<<$., Rest/binary>>, X, Y, ElfId, State) ->
+    parse_input(Rest, X+1, Y, ElfId, State);
+parse_input(<<$\n, Rest/binary>>, X, Y, ElfId, State) ->
+    parse_input(Rest, 0, Y+1, ElfId, State);
+parse_input(<<$#, Rest/binary>>, X, Y, ElfId, {ActiveElves, Positions}) ->
+    parse_input(Rest, X+1, Y, ElfId+1, {ActiveElves#{ElfId => {X, Y}}, Positions#{{X, Y} => ElfId}}).
+
+num_elves({_ActiveElves, Positions}) -> map_size(Positions).
+
+board_put(X, Y, Char, {W, Data}) ->
+    Index = Y * (W+1) + X,
+    Before = binary_part(Data, {0, Index}),
+    After = binary_part(Data, {Index + 1, byte_size(Data) - Index - 1}),
+    {W, <<Before/bytes, Char, After/bytes>>}.
+
+mkboard(W, H) ->
+    mkboard(W, H, <<>>).
+
+mkboard(W, 0, Acc) -> {W, Acc};
+mkboard(W, H, Acc) ->
+    MkRow = fun MkRow(0, R) -> R;
+                MkRow(N, R) -> MkRow(N-1, <<R/binary, $.>>) end,
+    WithRow = MkRow(W, Acc),
+    mkboard(W, H-1, <<WithRow/binary, $\n>>).
+
+render({_Active, Positions} = State) ->
+    {MinX, MaxX, MinY, MaxY} = get_bounds(State),
+    {_, Data} = maps:fold(fun ({X, Y}, Id, Board) -> board_put(X - MinX, Y - MinY, (Id rem 10) + $0, Board) end,
+              mkboard(MaxX - MinX + 1, MaxY - MinY + 1),
+              Positions),
+    Data.
+
+step(N, State) -> step(0, N, State).
+
+step(N, N, State) -> State;
+step(I, N, State) when N - I > 0 -> step(I+1, N, do_step(State, I)).
+
+do_step({ActiveElves, PositionsIn}, Round) ->
+    %io:format(" Stepping ~n", []),
+    %io:format("~s~n", [render({ActiveElves, PositionsIn})]),
+    {PlannedMoves, _Inactive} = plan_moves(ActiveElves, PositionsIn, Round),
+    maps:fold(fun (NewPos, ElfId, {Active, Positions}) ->
+                       #{ElfId := OldPos} = Active,
+                       Updooted = maps:remove(OldPos, Positions),
+                       {Active#{ElfId := NewPos}, Updooted#{NewPos => ElfId}}
+               end,
+               {ActiveElves, PositionsIn},
+               PlannedMoves).
+
+plan_moves(ActiveElves, Positions, Round) ->
+    {_Collisions, Moves, Inactive} =
+    maps:fold(
+      fun (ElfId, Position, {Collisions, MoveSet, Inactive}) ->
+              Move = get_move(Position, Positions, Round),
+              %io:format(" ~p ~p ~n", [ElfId, Position]),
+              %io:format(" ~p ~p ~n", [ElfId, Move]),
+              % Todo: only mark this unit as inactive if it exited because it had no neighbors (update the signature of get_move/2)
+              if 
+                  Position == Move ->
+                      {Collisions, MoveSet, Inactive#{ElfId => Position}};
+                  is_map_key(Move, Collisions) ->
+                      #{Move := Elves} = Collisions,
+                      {Collisions#{Move:=[ElfId|Elves]}, MoveSet, Inactive};
+                  is_map_key(Move, MoveSet) ->
+                      #{Move := CollidingElf} = MoveSet,
+                      {Collisions#{Move => [ElfId, CollidingElf]}, maps:remove(Move, MoveSet), Inactive};
+                  true ->
+                      {Collisions, MoveSet#{Move => ElfId}, Inactive}
+              end
+      end,
+      {#{}, #{}, #{}},
+      ActiveElves),
+    {Moves, Inactive}.
+
+
+open(Position, Positions) when is_map_key(Position, Positions) -> 0;
+open(_Position, _Positions) -> 1.
+
+% N S W NW SW E NE SE
+get_move({ElfX, ElfY}, Positions, Round) ->
+    [_|Adjacent] = [{X, Y} || X <- [ElfX, ElfX-1, ElfX+1], Y <- [ElfY, ElfY-1, ElfY+1]],
+    OpenByte= lists:foldl(fun (Pos, Acc) -> (Acc bsl 1) + open(Pos, Positions) end, 0, Adjacent),
+    %io:format("~.2B~n", [OpenByte]),
+    case Round rem 4 of
+        0 ->
+            if
+                2#11111111 == OpenByte -> {ElfX, ElfY};
+                2#10010010 == (OpenByte band 2#10010010) -> {ElfX, ElfY-1};
+                2#01001001 == (OpenByte band 2#01001001) -> {ElfX, ElfY+1};
+                2#00111000 == (OpenByte band 2#00111000) -> {ElfX-1, ElfY};
+                2#00000111 == (OpenByte band 2#00000111) -> {ElfX+1, ElfY};
+                true -> {ElfX, ElfY}
+            end;
+        1 ->
+            if
+                2#11111111 == OpenByte -> {ElfX, ElfY};
+                2#01001001 == (OpenByte band 2#01001001) -> {ElfX, ElfY+1};
+                2#00111000 == (OpenByte band 2#00111000) -> {ElfX-1, ElfY};
+                2#00000111 == (OpenByte band 2#00000111) -> {ElfX+1, ElfY};
+                2#10010010 == (OpenByte band 2#10010010) -> {ElfX, ElfY-1};
+                true -> {ElfX, ElfY}
+            end;
+        2 ->
+            if
+                2#11111111 == OpenByte -> {ElfX, ElfY};
+                2#00111000 == (OpenByte band 2#00111000) -> {ElfX-1, ElfY};
+                2#00000111 == (OpenByte band 2#00000111) -> {ElfX+1, ElfY};
+                2#10010010 == (OpenByte band 2#10010010) -> {ElfX, ElfY-1};
+                2#01001001 == (OpenByte band 2#01001001) -> {ElfX, ElfY+1};
+                true -> {ElfX, ElfY}
+            end;
+        3 ->
+            if
+                2#11111111 == OpenByte -> {ElfX, ElfY};
+                2#00000111 == (OpenByte band 2#00000111) -> {ElfX+1, ElfY};
+                2#10010010 == (OpenByte band 2#10010010) -> {ElfX, ElfY-1};
+                2#01001001 == (OpenByte band 2#01001001) -> {ElfX, ElfY+1};
+                2#00111000 == (OpenByte band 2#00111000) -> {ElfX-1, ElfY};
+                true -> {ElfX, ElfY}
+            end
+    end.
+
+mark_inactive(ElfId, {ActiveElves, Positions}) -> maps:remove(ElfId, ActiveElves).
+mark_active(ElfId, ElfPosition, {ActiveElves, Positions}) -> ActiveElves#{ElfId => ElfPosition}.
+
+get_bounds({_ActiveElves, Positions}) ->
+    maps:fold(fun ({X, Y}, _Value, {MinX, MaxX, MinY, MaxY}) ->
+                      {min(X, MinX), max(X, MaxX), min(Y, MinY), max(Y, MaxY)}
+              end,
+              {50000000, 0, 50000000, 0},
+              Positions).