remove a vec allocation from simulation step

src/marble_engine.rs

@@ -16,6 +16,7 @@ pub struct Machine {
 	board: Board,
 	marbles: Vec<Pos>,
 	powered: Vec<Pos>,
+	events: Vec<Event>,
 
 	input: Vec<u8>,
 	input_index: usize,
@@ -23,12 +24,27 @@ pub struct Machine {
 	steps: usize,
 }
 
+#[derive(Debug, Clone, Copy)]
+enum Event {
+	Stay,
+	/// (new_pos, new_dir)
+	MoveTo(Pos, Direction),
+	/// (new_pos, new_dir, trigger_pos)
+	Trigger(Pos, Direction, Pos),
+	/// (other, new_dir)
+	/// other marble should be set to reverse of new_dir
+	/// and should be cancelled if it had a movement event planned
+	Bounce(usize, Direction),
+	Remove,
+}
+
 impl Machine {
 	pub fn new_empty(input: Vec<u8>, width: usize) -> Self {
 		Self {
 			board: Board::new_empty(width, width),
 			marbles: Vec::new(),
 			powered: Vec::new(),
+			events: Vec::new(),
 			input,
 			input_index: 0,
 			output: Vec::new(),
@@ -113,39 +129,26 @@ impl Machine {
 			return;
 		}
 
-		#[derive(Debug, Clone, Copy)]
-		enum Event {
-			Stay,
-			/// (new_pos, new_dir)
-			MoveTo(Pos, Direction),
-			/// (new_pos, new_dir, trigger_pos)
-			Trigger(Pos, Direction, Pos),
-			/// (other, new_dir)
-			/// other marble should be set to reverse of new_dir
-			/// and should be cancelled if it had a movement event planned
-			Bounce(usize, Direction),
-			Remove,
-		}
-
-		let mut marble_events: Vec<Event> = self
-			.marbles
-			.iter()
-			.map(|&pos| {
+		self.events.clear();
+		for &pos in &self.marbles {
 			let marble = self.board.get(pos).unwrap();
 			let Tile::Marble { value, dir } = marble else {
 				panic!("broken marble");
 			};
 			let front_pos = dir.step(pos);
 			let Some(front_tile) = self.board.get(front_pos) else {
-					return Event::Stay;
+				self.events.push(Event::Stay);
+				continue;
 			};
 
 			if let Tile::Powerable(PTile::Bag, _) = front_tile {
-					return Event::Remove;
+				self.events.push(Event::Remove);
+				continue;
 			}
 			if let Tile::Powerable(PTile::IO, _) = front_tile {
 				self.output.push(value as u8);
-					return Event::Remove;
+				self.events.push(Event::Remove);
+				continue;
 			}
 
 			let can_move_to = |tile| matches!(tile, Some(Tile::Blank | Tile::Digit(_)));
@@ -172,8 +175,7 @@ impl Machine {
 				}
 				_ => None,
 			};
-
-				if can_move_to(Some(front_tile)) {
+			let e = if can_move_to(Some(front_tile)) {
 				Event::MoveTo(front_pos, dir)
 			} else if let Tile::Powerable(PTile::Trigger, _) = front_tile {
 				let target_pos = dir.step(front_pos);
@@ -200,29 +202,29 @@ impl Machine {
 				}
 			} else {
 				Event::Stay
+			};
+			self.events.push(e);
 		}
-			})
-			.collect();
 
 		// resolve bounces
-		for i in 0..marble_events.len() {
-			let event = marble_events[i];
+		for i in 0..self.events.len() {
+			let event = self.events[i];
 			if let Event::Bounce(other_index, dir) = event {
-				match marble_events[other_index] {
+				match self.events[other_index] {
 					// cancel bounces on marble that are about to disappear
 					Event::Remove => {
-						marble_events[i] = Event::MoveTo(self.marbles[other_index], dir.opposite())
+						self.events[i] = Event::MoveTo(self.marbles[other_index], dir.opposite())
 					}
 					// let already bouncing marbles continue
 					Event::Bounce(_, _) => (),
 					// interrupt any other movement/staying to bounce
-					_ => marble_events[other_index] = Event::Bounce(i, dir.opposite()),
+					_ => self.events[other_index] = Event::Bounce(i, dir.opposite()),
 				}
 			}
 		}
 
 		// resolve deletions of tiles
-		for (i, event) in marble_events.iter().enumerate() {
+		for (i, event) in self.events.iter().enumerate() {
 			if let Event::Remove = event {
 				self.board.set(self.marbles[i], Tile::Blank);
 			}
@@ -230,7 +232,7 @@ impl Machine {
 
 		// resolve triggers
 		let mut triggers_activated = Vec::new();
-		for event in &mut marble_events {
+		for event in &mut self.events {
 			if let Event::Trigger(new_pos, dir, trigger_pos) = event {
 				triggers_activated.push(*trigger_pos);
 				*event = Event::MoveTo(*new_pos, *dir);
@@ -238,10 +240,10 @@ impl Machine {
 		}
 
 		// resolve collisions (multiple marbles entering the same space)
-		for i in 0..(marble_events.len() - 1) {
-			let event = marble_events[i];
+		for i in 0..(self.events.len() - 1) {
+			let event = self.events[i];
 			if let Event::MoveTo(new_pos, _dir) = event {
-				for other_event in &mut marble_events[(i + 1)..] {
+				for other_event in &mut self.events[(i + 1)..] {
 					if let Event::MoveTo(other_pos, _other_dir) = other_event {
 						// todo: maybe sort by direction so the sucessful direction is consistent
 						if other_pos == &new_pos {
@@ -253,7 +255,7 @@ impl Machine {
 		}
 
 		// resolve movement
-		for (i, &event) in marble_events.iter().enumerate() {
+		for (i, &event) in self.events.iter().enumerate() {
 			if let Event::Remove = event {
 				continue;
 			}
@@ -281,7 +283,7 @@ impl Machine {
 		}
 
 		// resolve deletions of marbles
-		for (i, event) in marble_events.iter().enumerate().rev() {
+		for (i, event) in self.events.iter().enumerate().rev() {
 			if let Event::Remove = event {
 				self.marbles.remove(i);
 			}