tiny mini optimizations

aoc_2024/src/day21.rs

@@ -12,13 +12,7 @@ impl Path {
         let mut path = [None, None, None, None, None, None];
         let mut i = 0;
         while i < steps {
-            path[i] = Some(match buttons[i] {
-                DirButton::Up => DirButton::Up,
-                DirButton::Down => DirButton::Down,
-                DirButton::Left => DirButton::Left,
-                DirButton::Right => DirButton::Right,
-                DirButton::A => DirButton::A,
-            });
+            path[i] = Some(buttons[i]);
             i += 1;
         }
         let steps = steps + 1;
@@ -123,7 +117,7 @@ const DIRBUTTON_PATHS: [[[Option<Path>; 2]; 5]; 5] = [
 ];
 
 impl DirButton {
-    fn index(&self) -> usize {
+    const fn index(&self) -> usize {
         match self {
             DirButton::Up => 0,
             DirButton::Down => 1,
@@ -133,7 +127,7 @@ impl DirButton {
         }
     }
 
-    fn to(&self, other: &DirButton) -> &[Option<Path>; 2] {
+    const fn paths_to(&self, other: &DirButton) -> &[Option<Path>; 2] {
         &DIRBUTTON_PATHS[self.index()][other.index()]
     }
 }
@@ -154,7 +148,7 @@ enum NumButton {
 }
 
 impl NumButton {
-    fn pos(&self) -> (usize, usize) {
+    const fn pos(&self) -> (usize, usize) {
         match self {
             NumButton::One => (0, 2),
             NumButton::Two => (1, 2),
@@ -170,7 +164,7 @@ impl NumButton {
         }
     }
 
-    fn to(&self, other: &NumButton) -> [Option<Path>; 2] {
+    fn paths_to(&self, other: &NumButton) -> [Option<Path>; 2] {
         let start = self.pos();
         let end = other.pos();
 
@@ -247,7 +241,7 @@ impl NumButton {
     }
 }
 
-type Input = Vec<(usize, Vec<NumButton>)>;
+type Input = Vec<(DistanceSize, Vec<NumButton>)>;
 
 #[aoc_generator(day21)]
 fn parse(input: &str) -> Input {
@@ -277,7 +271,8 @@ fn parse(input: &str) -> Input {
         .collect()
 }
 
-type DistanceMatrix = [[usize; 5]; 5];
+type DistanceSize = u64;
+type DistanceMatrix = [[DistanceSize; 5]; 5];
 
 fn precompute_steps(steps: &mut [DistanceMatrix]) {
     if steps.len() == 1 {
@@ -297,7 +292,7 @@ fn precompute_steps(steps: &mut [DistanceMatrix]) {
     buttons.iter().for_each(|start| {
         buttons.iter().for_each(|end| {
             steps[0][start.index()][end.index()] = start
-                .to(end)
+                .paths_to(end)
                 .iter()
                 .flatten()
                 .map(|path| {
@@ -309,46 +304,41 @@ fn precompute_steps(steps: &mut [DistanceMatrix]) {
                         })
                         .0
                 })
-                .fold(usize::MAX, |acc, next| acc.min(next));
+                .fold(DistanceSize::MAX, |acc, next| acc.min(next));
         });
     });
 }
 
-fn shortest_dir_path(path: Path, steps: &mut [DistanceMatrix]) -> usize {
+fn shortest_dir_path(path: Path, steps: &mut [DistanceMatrix]) -> DistanceSize {
     path.path
         .iter()
         .flatten()
         .fold((0, &DirButton::A), |acc, next| {
-            let sum = acc.0;
-            let pos = acc.1;
-
-            let extension = steps[0][pos.index()][next.index()];
-
-            (sum + extension, next)
+            (acc.0 + steps[0][acc.1.index()][next.index()], next)
         })
         .0
 }
 
-fn shortest_path(path: &[NumButton], steps: &mut [DistanceMatrix]) -> usize {
+fn shortest_path(path: &[NumButton], steps: &mut [DistanceMatrix]) -> DistanceSize {
     path.iter()
         .fold((0, &NumButton::A), |acc, end| {
-            let sum = acc.0;
-            let start = acc.1;
-
-            let extension = start
-                .to(end)
+            (
+                acc.0
+                    + acc
+                        .1
+                        .paths_to(end)
                         .into_iter()
                         .flatten()
                         .map(|path| shortest_dir_path(path, steps))
-                .min()
-                .unwrap();
-            (sum + extension, end)
+                        .fold(DistanceSize::MAX, |acc, next| acc.min(next)),
+                end,
+            )
         })
         .0
 }
 
 #[aoc(day21, part1)]
-fn part1(input: &Input) -> usize {
+fn part1(input: &Input) -> DistanceSize {
     let mut steps = vec![[[1; 5]; 5]; 3];
 
     precompute_steps(&mut steps);
@@ -360,7 +350,7 @@ fn part1(input: &Input) -> usize {
 }
 
 #[aoc(day21, part2)]
-fn part2(input: &Input) -> usize {
+fn part2(input: &Input) -> DistanceSize {
     let mut steps = vec![[[1; 5]; 5]; 26];
 
     precompute_steps(&mut steps);