day09: Chage stuff for part 2

Part 1 was missing the "y_diff.abs() == x_diff.abs()" condition in
Pos.move_after(), which made the program show the wrong output at first.

day09/src/main.rs

@@ -40,7 +40,9 @@ impl Pos {
 			return
 		}
 
-		if x_diff.abs() > y_diff.abs() {
+		if x_diff.abs() == y_diff.abs() {
+			self.move_((x_diff.abs() - 1) * x_diff.signum(), (y_diff.abs() - 1) * y_diff.signum());
+		} else if x_diff.abs() > y_diff.abs() {
 			self.move_((x_diff.abs() - 1) * x_diff.signum(), y_diff);
 		} else {
 			self.move_(x_diff, (y_diff.abs() - 1) * y_diff.signum());
@@ -56,8 +58,11 @@ fn main() -> Result<(), Box<dyn error::Error>> {
 	let f = File::open("input.txt")?;
 	let reader = BufReader::new(f);
 
-	let mut h_pos = Pos { x: 0, y: 0 };
-	let mut t_pos = Pos { x: 0, y: 0 };
+	let mut knot_positions = vec![];
+	for _ in 0..10 {
+		knot_positions.push(Pos { x: 0, y: 0 });
+	}
+
 	let mut visited_locations = HashSet::new();
 	for line in reader.lines() {
 		let line = line?;
@@ -65,13 +70,16 @@ fn main() -> Result<(), Box<dyn error::Error>> {
 		let direction = s_iter.next().ok_or(format!("Could not split {line} on whitespace"))?;
 		let amount: i32 = s_iter.next().ok_or(format!("Could not split {line} into 2 parts."))?.parse()?;
 		for _ in 0..amount {
-			h_pos.move_into_direction(direction)?;
-			t_pos.move_after(&h_pos);
+			knot_positions[0].move_into_direction(direction)?;
+			for i in 1..knot_positions.len() {
+				let (head, tail) = knot_positions.split_at_mut(i);
+				tail[0].move_after(head.last().ok_or("head doesn't have an element")?);
+			}
 			if DEBUG {
-				h_pos.show();
-				t_pos.show();
+				knot_positions[0].show();
+				knot_positions[9].show();
 			}
-			visited_locations.insert((t_pos.x.to_owned(), t_pos.y.to_owned()));
+			visited_locations.insert((knot_positions[9].x.to_owned(), knot_positions[9].y.to_owned()));
 		}
 		if DEBUG {
 			println!("");