tiny mini optimizations

aoc_2024/src/day20.rs

@@ -42,7 +42,6 @@ fn parse(input: &str) -> Input {
 #[aoc(day20, part1)]
 fn part1(input: &Input) -> usize {
     let start = input.0;
-    let end = input.1;
     let map = &input.2;
 
     #[cfg(not(test))]
@@ -124,7 +123,6 @@ fn part1(input: &Input) -> usize {
 #[aoc(day20, part2)]
 fn part2(input: &Input) -> usize {
     let start = input.0;
-    let end = input.1;
     let map = &input.2;
 
     #[cfg(not(test))]

aoc_2024/src/day21.rs

@@ -1,56 +1,23 @@
 use aoc_runner_derive::{aoc, aoc_generator};
 
-#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+#[derive(Debug, PartialEq, Eq)]
 struct Path {
     steps: usize,
     path: [Option<DirButton>; 6],
 }
 
 impl Path {
-    fn new() -> Self {
+    const fn from(buttons: &[DirButton]) -> Option<Self> {
-        Self {
+        let steps = buttons.len();
-            steps: 0,
+        let mut path = [None, None, None, None, None, None];
-            path: [None, None, None, None, None, None],
+        let mut i = 0;
+        while i < steps {
+            path[i] = Some(buttons[i]);
+            i += 1;
         }
-    }
+        let steps = steps + 1;
-
+        path[i] = Some(DirButton::A);
-    fn push(&mut self, button: DirButton) {
+        Some(Self { steps, path })
-        self.path[self.steps] = Some(button);
-        self.steps += 1;
-    }
-
-    fn append(&mut self, other: &Self) {
-        for i in 0..other.steps {
-            self.push(other.path[i].unwrap());
-        }
-    }
-
-    fn reversed(&self) -> Self {
-        let mut path = [None; 6];
-        (0..self.steps).for_each(|i| {
-            path[i] = match self.path[self.steps - i - 1] {
-                Some(DirButton::Up) => Some(DirButton::Down),
-                Some(DirButton::Down) => Some(DirButton::Up),
-                Some(DirButton::Left) => Some(DirButton::Right),
-                Some(DirButton::Right) => Some(DirButton::Left),
-                Some(DirButton::A) => Some(DirButton::A),
-                None => None,
-            };
-        });
-
-        Self {
-            steps: self.steps,
-            path,
-        }
-    }
-}
-
-impl IntoIterator for Path {
-    type Item = DirButton;
-    type IntoIter = std::iter::Flatten<std::array::IntoIter<Option<DirButton>, 6>>;
-
-    fn into_iter(self) -> Self::IntoIter {
-        self.path.into_iter().flatten()
     }
 }
 
@@ -63,18 +30,94 @@ enum DirButton {
     A,
 }
 
-impl DirButton {
+const DIRBUTTON_PATHS: [[[Option<Path>; 2]; 5]; 5] = [
-    fn pos(&self) -> (usize, usize) {
+    // Up
-        match self {
+    [
-            DirButton::Up => (1, 0),
+        // Up
-            DirButton::Down => (1, 1),
+        [Path::from(&[]), None],
-            DirButton::Left => (0, 1),
+        // Down
-            DirButton::Right => (2, 1),
+        [Path::from(&[DirButton::Down]), None],
-            DirButton::A => (2, 0),
+        // Left
-        }
+        [Path::from(&[DirButton::Down, DirButton::Left]), None],
-    }
+        // Right
+        [
+            Path::from(&[DirButton::Down, DirButton::Right]),
+            Path::from(&[DirButton::Right, DirButton::Down]),
+        ],
+        // A
+        [Path::from(&[DirButton::Right]), None],
+    ],
+    // Down
+    [
+        // Up
+        [Path::from(&[DirButton::Up]), None],
+        // Down
+        [Path::from(&[]), None],
+        // Left
+        [Path::from(&[DirButton::Left]), None],
+        // Right
+        [Path::from(&[DirButton::Right]), None],
+        // A
+        [
+            Path::from(&[DirButton::Up, DirButton::Right]),
+            Path::from(&[DirButton::Right, DirButton::Up]),
+        ],
+    ],
+    // Left
+    [
+        // Up
+        [Path::from(&[DirButton::Right, DirButton::Up]), None],
+        // Down
+        [Path::from(&[DirButton::Right]), None],
+        // Left
+        [Path::from(&[]), None],
+        // Right
+        [Path::from(&[DirButton::Right, DirButton::Right]), None],
+        // A
+        [
+            Path::from(&[DirButton::Right, DirButton::Right, DirButton::Up]),
+            None,
+        ],
+    ],
+    // Right
+    [
+        // Up
+        [
+            Path::from(&[DirButton::Up, DirButton::Left]),
+            Path::from(&[DirButton::Left, DirButton::Up]),
+        ],
+        // Down
+        [Path::from(&[DirButton::Left]), None],
+        // Left
+        [Path::from(&[DirButton::Left, DirButton::Left]), None],
+        // Right
+        [Path::from(&[]), None],
+        // A
+        [Path::from(&[DirButton::Up]), None],
+    ],
+    // A
+    [
+        // Up
+        [Path::from(&[DirButton::Left]), None],
+        // Down
+        [
+            Path::from(&[DirButton::Down, DirButton::Left]),
+            Path::from(&[DirButton::Left, DirButton::Down]),
+        ],
+        // Left
+        [
+            Path::from(&[DirButton::Down, DirButton::Left, DirButton::Left]),
+            None,
+        ],
+        // Right
+        [Path::from(&[DirButton::Down]), None],
+        // A
+        [Path::from(&[]), None],
+    ],
+];
 
-    fn index(&self) -> usize {
+impl DirButton {
+    const fn index(&self) -> usize {
         match self {
             DirButton::Up => 0,
             DirButton::Down => 1,
@@ -84,44 +127,12 @@ impl DirButton {
         }
     }
 
-    fn to(&self, other: &DirButton) -> [Option<Path>; 2] {
+    const fn paths_to(&self, other: &DirButton) -> &[Option<Path>; 2] {
-        let start = self.pos();
+        &DIRBUTTON_PATHS[self.index()][other.index()]
-        let end = other.pos();
-
-        let mut x = Path::new();
-        let mut y = Path::new();
-
-        if start.0 < end.0 {
-            (start.0..end.0).for_each(|_| x.push(DirButton::Right));
-        } else {
-            (end.0..start.0).for_each(|_| x.push(DirButton::Left));
-        };
-        if start.1 < end.1 {
-            (start.1..end.1).for_each(|_| y.push(DirButton::Down));
-        } else {
-            (end.1..start.1).for_each(|_| y.push(DirButton::Up));
-        };
-
-        if start.0 == 0 && end.1 == 0 {
-            x.append(&y);
-            x.push(DirButton::A);
-            [Some(x), None]
-        } else if end.0 == 0 && start.1 == 0 {
-            y.append(&x);
-            y.push(DirButton::A);
-            [Some(y), None]
-        } else {
-            let x_copy = x;
-            x.append(&y);
-            x.push(DirButton::A);
-            y.append(&x_copy);
-            y.push(DirButton::A);
-            [Some(x), Some(y)]
-        }
     }
 }
 
-#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+#[derive(Debug, PartialEq, Eq)]
 enum NumButton {
     One,
     Two,
@@ -137,7 +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),
@@ -153,45 +164,84 @@ impl NumButton {
         }
     }
 
-    #[inline(always)]
+    fn paths_to(&self, other: &NumButton) -> [Option<Path>; 2] {
-    fn to(&self, other: &NumButton) -> [Option<Path>; 2] {
         let start = self.pos();
         let end = other.pos();
 
-        let mut x = Path::new();
+        let bx = if start.0 < end.0 {
-        let mut y = Path::new();
+            DirButton::Right
+        } else {
+            DirButton::Left
+        };
+        let dx = start.0.abs_diff(end.0);
 
-        if start.0 < end.0 {
+        let by = if start.1 < end.1 {
-            (start.0..end.0).for_each(|_| x.push(DirButton::Right));
+            DirButton::Down
         } else {
-            (end.0..start.0).for_each(|_| x.push(DirButton::Left));
+            DirButton::Up
-        };
-        if start.1 < end.1 {
-            (start.1..end.1).for_each(|_| y.push(DirButton::Down));
-        } else {
-            (end.1..start.1).for_each(|_| y.push(DirButton::Up));
         };
+        let dy = start.1.abs_diff(end.1);
 
         if start.0 == 0 && end.1 == 3 {
-            x.append(&y);
+            let mut x = [None, None, None, None, None, None];
-            x.push(DirButton::A);
+            (0..dx).for_each(|i| {
-            [Some(x), None]
+                x[i] = Some(bx);
+            });
+            (0..dy).for_each(|i| {
+                x[i + dx] = Some(by);
+            });
+            x[dx + dy] = Some(DirButton::A);
+            [
+                Some(Path {
+                    steps: dx + dy + 1,
+                    path: x,
+                }),
+                None,
+            ]
         } else if end.0 == 0 && start.1 == 3 {
-            y.append(&x);
+            let mut y = [None, None, None, None, None, None];
-            y.push(DirButton::A);
+            (0..dx).for_each(|i| {
-            [Some(y), None]
+                y[i + dy] = Some(bx);
+            });
+            (0..dy).for_each(|i| {
+                y[i] = Some(by);
+            });
+            y[dx + dy] = Some(DirButton::A);
+            [
+                Some(Path {
+                    steps: dx + dy + 1,
+                    path: y,
+                }),
+                None,
+            ]
         } else {
-            let x_copy = x;
+            let mut x = [None, None, None, None, None, None];
-            x.append(&y);
+            let mut y = [None, None, None, None, None, None];
-            x.push(DirButton::A);
+            (0..dx).for_each(|i| {
-            y.append(&x_copy);
+                x[i] = Some(bx);
-            y.push(DirButton::A);
+                y[i + dy] = Some(bx);
-            [Some(x), Some(y)]
+            });
+            (0..dy).for_each(|i| {
+                x[i + dx] = Some(by);
+                y[i] = Some(by);
+            });
+            x[dx + dy] = Some(DirButton::A);
+            y[dx + dy] = Some(DirButton::A);
+            [
+                Some(Path {
+                    steps: dx + dy + 1,
+                    path: x,
+                }),
+                Some(Path {
+                    steps: dx + dy + 1,
+                    path: y,
+                }),
+            ]
         }
     }
 }
 
-type Input = Vec<(usize, Vec<NumButton>)>;
+type Input = Vec<(DistanceSize, Vec<NumButton>)>;
 
 #[aoc_generator(day21)]
 fn parse(input: &str) -> Input {
@@ -221,7 +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 {
@@ -238,106 +289,74 @@ fn precompute_steps(steps: &mut [DistanceMatrix]) {
         DirButton::A,
     ];
 
-    buttons.iter().enumerate().for_each(|(i, start)| {
+    buttons.iter().for_each(|start| {
-        buttons[i + 1..].iter().for_each(|end| {
+        buttons.iter().for_each(|end| {
-            let (forward, reversed) = start
+            steps[0][start.index()][end.index()] = start
-                .to(end)
+                .paths_to(end)
-                .into_iter()
+                .iter()
                 .flatten()
-                .map(|mut path| {
+                .map(|path| {
-                    path.steps -= 1;
+                    path.path
-                    let mut reversed = path.reversed();
+                        .iter()
-                    let mut forward = path;
-                    reversed.push(DirButton::A);
-                    forward.push(DirButton::A);
-
-                    (
-                        forward
-                            .path
-                            .into_iter()
                         .flatten()
-                            .fold((0, DirButton::A), |acc, next| {
+                        .fold((0, &DirButton::A), |acc, next| {
-                                let extension = steps[1][acc.1.index()][next.index()];
+                            (acc.0 + steps[1][acc.1.index()][next.index()], next)
-
-                                (acc.0 + extension, next)
                         })
-                            .0,
+                        .0
-                        reversed
-                            .path
-                            .into_iter()
-                            .flatten()
-                            .fold((0, DirButton::A), |acc, next| {
-                                let extension = steps[1][acc.1.index()][next.index()];
-
-                                (acc.0 + extension, next)
                 })
-                            .0,
+                .fold(DistanceSize::MAX, |acc, next| acc.min(next));
-                    )
-                })
-                .fold((usize::MAX, usize::MAX), |acc, next| {
-                    (acc.0.min(next.0), acc.1.min(next.1))
-                });
-            steps[0][start.index()][end.index()] = forward;
-            steps[0][end.index()][start.index()] = reversed;
         });
     });
 }
 
-fn shortest_dir_path(path: Path, steps: &mut [DistanceMatrix]) -> usize {
+fn shortest_dir_path(path: Path, steps: &mut [DistanceMatrix]) -> DistanceSize {
     path.path
-        .into_iter()
+        .iter()
         .flatten()
-        .fold((0, DirButton::A), |acc, next| {
+        .fold((0, &DirButton::A), |acc, next| {
-            let sum = acc.0;
+            (acc.0 + steps[0][acc.1.index()][next.index()], next)
-            let pos = acc.1;
-
-            let extension = steps[0][pos.index()][next.index()];
-
-            (sum + extension, next)
         })
         .0
 }
 
-fn shortest_path(path: Vec<NumButton>, steps: &mut [DistanceMatrix]) -> usize {
+fn shortest_path(path: &[NumButton], steps: &mut [DistanceMatrix]) -> DistanceSize {
-    path.into_iter()
+    path.iter()
-        .fold((0, NumButton::A), |acc, end| {
+        .fold((0, &NumButton::A), |acc, end| {
-            let sum = acc.0;
+            (
-            let start = acc.1;
+                acc.0
-
+                    + acc
-            let extension = start
+                        .1
-                .to(&end)
+                        .paths_to(end)
                         .into_iter()
                         .flatten()
                         .map(|path| shortest_dir_path(path, steps))
-                .min()
+                        .fold(DistanceSize::MAX, |acc, next| acc.min(next)),
-                .unwrap();
+                end,
-            (sum + extension, 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);
 
     input
         .iter()
-        .cloned()
         .map(|(num, path)| num * shortest_path(path, &mut steps))
         .sum()
 }
 
 #[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);
 
     input
         .iter()
-        .cloned()
         .map(|(num, path)| num * shortest_path(path, &mut steps))
         .sum()
 }