day14: some silly and not super effective performance optimizations

14/src/main.rs

@@ -31,51 +31,57 @@ fn main() {
 #[derive(Debug)]
 struct Platform {
     rows: Vec<Vec<char>>,
+    width: usize,
+    height: usize,
 }
 
 impl<T: BufRead> From<Lines<T>> for Platform {
     fn from(lines: Lines<T>) -> Self {
+        let rows: Vec<Vec<char>> = lines.map(|line| line.unwrap().chars().collect()).collect();
+        let width = rows[0].len();
+        let height = rows.len();
         Self {
-            rows: lines.map(|line| line.unwrap().chars().collect()).collect(),
+            rows,
+            width,
+            height,
         }
     }
 }
 
-enum Direction {
-    North,
-    South,
-    East,
-    West,
-}
-
 #[derive(Debug, PartialEq)]
 enum Axis {
     Rows,
     Columns,
 }
 
-impl Direction {
+struct North;
-    fn reverse_direction(&self) -> bool {
+struct South;
-        match self {
+struct East;
-            Direction::North | Direction::West => false,
+struct West;
-            Direction::South | Direction::East => true,
+
+trait Direction {
+    const REVERSED: bool;
+    const AXIS: Axis;
 }
+
+impl Direction for North {
+    const REVERSED: bool = false;
+    const AXIS: Axis = Axis::Columns;
 }
-    fn axis(&self) -> Axis {
+impl Direction for South {
-        match self {
+    const REVERSED: bool = true;
-            Direction::North | Direction::South => Axis::Columns,
+    const AXIS: Axis = Axis::Columns;
-            Direction::East | Direction::West => Axis::Rows,
 }
+impl Direction for East {
+    const REVERSED: bool = true;
+    const AXIS: Axis = Axis::Rows;
 }
+impl Direction for West {
+    const REVERSED: bool = false;
+    const AXIS: Axis = Axis::Rows;
 }
 
 impl<'a> Platform {
-    fn width(&self) -> usize {
-        self.rows[0].len()
-    }
-    fn height(&self) -> usize {
-        self.col(0).len()
-    }
     fn col(&self, col: usize) -> Vec<char> {
         self.rows.iter().map(|row| row[col]).collect()
     }
@@ -84,97 +90,94 @@ impl<'a> Platform {
             self.rows[row_idx][idx] = col[row_idx];
         }
     }
-    fn roll(&mut self, dir: &Direction) {
+    fn roll<T: Direction>(&mut self) {
-        match dir.axis() {
+        match T::AXIS {
             Axis::Columns => {
-                for idx in 0..self.width() {
+                for idx in 0..self.width {
-                    self.roll_one(idx, dir)
+                    let new = self.roll_one::<T>(idx);
+                    self.replace_col(idx, new);
                 }
             }
-
             Axis::Rows => {
-                for idx in 0..self.height() {
+                for idx in 0..self.height {
-                    self.roll_one(idx, dir)
+                    let new = self.roll_one::<T>(idx);
+                    self.rows[idx].copy_from_slice(new.as_slice());
                 }
             }
         }
     }
-    fn roll_rock_at(old: &mut Vec<char>, inner_idx: usize, dir: &Direction) {
+    fn roll_rock_at<T: Direction>(old: &mut Vec<char>, inner_idx: usize) {
         // Find the first # rock or the edge of the map, we can't look beyond this for a resting position
-        match dir.reverse_direction() {
+        if T::REVERSED {
-            true => {
+            // The furthest possible resting position is the first # below us, or the edge of the map
-                let upper_limit = (inner_idx..old.len())
+            let upper_limit = (inner_idx..old.len() - 1)
                 .find(|c| old[*c] == '#')
                 .unwrap_or(old.len());
 
-                if let Some(empty_pos) = (inner_idx..upper_limit).filter(|i| old[*i] == '.').last()
+            // We will roll to the position of the furthest '.' before the upper limit
-                {
+            if let Some(empty_pos) = (inner_idx..upper_limit).rev().find(|i| old[*i] == '.') {
                 old.swap(inner_idx, empty_pos);
             }
-            }
+        } else {
-            false => {
+            // the furthest possible resting position is the first # above us, or the edge
-                // Find the first # rock or the edge of the map, we can't look beyond this for a resting position
             let lower_limit = (0..inner_idx).rev().find(|c| old[*c] == '#').unwrap_or(0);
 
-                if let Some(empty_pos) = (lower_limit..inner_idx)
+            // We will roll to the position of the furthest '.' before the lower limit
-                    .rev()
+            if let Some(empty_pos) = (lower_limit..inner_idx).find(|i| old[*i] == '.') {
-                    .filter(|i| old[*i] == '.')
-                    .last()
-                {
                 old.swap(inner_idx, empty_pos);
             }
         }
     }
-    }
+
-    fn roll_one(&mut self, idx: usize, dir: &Direction) {
+    fn roll_one<T: Direction>(&mut self, idx: usize) -> Vec<char> {
-        let mut old = match dir.axis() {
+        let mut old = match T::AXIS {
             Axis::Columns => self.col(idx),
             Axis::Rows => self.rows[idx].clone(),
         };
-        let idx_iter: Either<_, _> = match dir.reverse_direction() {
+        let idx_iter: Either<_, _> = match T::REVERSED {
             true => Either::Left((0..old.len()).rev()),
             false => Either::Right(0..old.len()),
         };
+        let end_idx = if T::REVERSED { old.len() } else { 0 };
         for inner_idx in idx_iter {
             match old[inner_idx] {
                 '.' | '#' => continue,
-                'O' if dir.reverse_direction() && inner_idx == old.len() => continue,
+                'O' if inner_idx == end_idx => continue,
-                'O' if !dir.reverse_direction() && inner_idx == 0 => continue,
+                'O' => Self::roll_rock_at::<T>(&mut old, inner_idx),
-                'O' => Self::roll_rock_at(&mut old, inner_idx, dir),
                 _ => panic!("invalid character"),
             }
         }
-        match dir.axis() {
+        old
-            Axis::Columns => self.replace_col(idx, old),
+    }
-            Axis::Rows => self.rows[idx] = old,
+    fn score<T: Direction>(&self) -> u64 {
+        match T::AXIS {
+            Axis::Columns => self.score_columns::<T>(),
+            Axis::Rows => self.score_rows::<T>(),
         }
     }
-    fn score(&self, dir: &Direction) -> u64 {
+    fn row_or_column_score<T: Direction>(&self, idx: usize) -> usize {
-        match dir.axis() {
+        if T::REVERSED {
-            Axis::Columns => self.score_columns(dir),
-            Axis::Rows => self.score_rows(dir),
-        }
-    }
-    fn row_or_column_score(&self, idx: usize, dir: &Direction) -> usize {
-        if dir.reverse_direction() {
             idx + 1
         } else {
-            self.rows.len() - idx
+            match T::AXIS {
+                Axis::Rows => self.width - idx,
+                Axis::Columns => self.height - idx,
             }
         }
-    fn score_columns(&self, dir: &Direction) -> u64 {
+    }
-        (0..self.height())
+    fn score_columns<T: Direction>(&self) -> u64 {
+        (0..self.height)
             .map(|row| {
                 self.rows[row].iter().filter(|c| **c == 'O').count()
-                    * self.row_or_column_score(row, dir)
+                    * self.row_or_column_score::<T>(row)
             })
             .sum::<usize>() as u64
     }
     fn roll_cycle(&mut self) {
-        self.roll(&Direction::North);
+        self.roll::<North>();
-        self.roll(&Direction::West);
+        self.roll::<West>();
-        self.roll(&Direction::South);
+        self.roll::<South>();
-        self.roll(&Direction::East);
+        self.roll::<East>();
     }
 
     // find the first loop, return the iteration count when we first saw it and when we saw it again
@@ -190,7 +193,7 @@ impl<'a> Platform {
             }
         }
     }
-    fn score_rows(&self, dir: &Direction) -> u64 {
+    fn score_rows<T: Direction>(&self) -> u64 {
         unimplemented!()
     }
 }
@@ -211,8 +214,8 @@ impl Display for Platform {
 
 fn problem1<T: BufRead>(input: Lines<T>) -> u64 {
     let mut p = Platform::from(input);
-    p.roll(&Direction::North);
+    p.roll::<North>();
-    p.score(&Direction::North)
+    p.score::<North>()
 }
 
 // PROBLEM 2 solution
@@ -223,11 +226,12 @@ fn problem2<T: BufRead>(input: Lines<T>) -> u64 {
     let loop_length = first_loop.1 - first_loop.0;
     let cycles_to_skip = ((ITERATIONS - first_loop.0) / loop_length) * loop_length;
     let iterations_remaining = ITERATIONS - first_loop.0 - cycles_to_skip;
+
     for _ in 0..iterations_remaining {
         p.roll_cycle();
     }
 
-    p.score(&Direction::North)
+    p.score::<North>()
 }
 
 #[cfg(test)]