day21 fast

aoc_2024/src/day20.rs

@@ -0,0 +1,256 @@
+use std::usize;
+
+use aoc_runner_derive::{aoc, aoc_generator};
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+enum Cell {
+    Empty,
+    Wall,
+}
+
+type Input = ((usize, usize), (usize, usize), Vec<Vec<Cell>>);
+
+#[aoc_generator(day20)]
+fn parse(input: &str) -> Input {
+    let mut start = (0, 0);
+    let mut end = (0, 0);
+    let map = input
+        .lines()
+        .enumerate()
+        .map(|(y, line)| {
+            line.chars()
+                .enumerate()
+                .map(|(x, c)| match c {
+                    '.' => Cell::Empty,
+                    '#' => Cell::Wall,
+                    'S' => {
+                        start = (x, y);
+                        Cell::Empty
+                    }
+                    'E' => {
+                        end = (x, y);
+                        Cell::Empty
+                    }
+                    _ => panic!("unexpected character: {}", c),
+                })
+                .collect()
+        })
+        .collect();
+    (start, end, map)
+}
+
+#[aoc(day20, part1)]
+fn part1(input: &Input) -> usize {
+    let start = input.0;
+    let end = input.1;
+    let map = &input.2;
+
+    #[cfg(not(test))]
+    let min_saving = 100;
+    #[cfg(test)]
+    let min_saving = 2;
+
+    let w = map[0].len();
+    let h = map.len();
+
+    let mut dist = vec![vec![usize::MAX; w]; h];
+    dist[start.1][start.0] = 0;
+
+    let mut deque = std::collections::VecDeque::new();
+    deque.push_back((0, start));
+
+    while let Some((d, pos)) = deque.pop_front() {
+        if dist[pos.1][pos.0] < d {
+            continue;
+        }
+
+        dist[pos.1][pos.0] = d;
+
+        [(1, 0), (-1, 0), (0, -1), (0, 1)]
+            .iter()
+            .for_each(|(dx, dy)| {
+                let x = (pos.0 as isize + dx) as usize;
+                let y = (pos.1 as isize + dy) as usize;
+
+                if x < w && y < h && map[y][x] == Cell::Empty {
+                    let new_d = d + 1;
+                    if new_d < dist[y][x] {
+                        deque.push_back((new_d, (x, y)));
+                    }
+                }
+            })
+    }
+
+    map.iter()
+        .enumerate()
+        .map(|(y, line)| {
+            line.iter()
+                .enumerate()
+                .map(|(x, cell)| {
+                    let y = y as isize;
+                    if *cell == Cell::Empty {
+                        [
+                            (0, 2),
+                            (0, -2),
+                            (2, 0),
+                            (-2, 0),
+                            (1, 1),
+                            (1, -1),
+                            (-1, 1),
+                            (-1, -1),
+                        ]
+                        .iter()
+                        .filter(|(dx, dy)| {
+                            let nx = x as isize + dx;
+                            let ny = y + dy;
+                            nx >= 0
+                                && nx < w as isize
+                                && ny >= 0
+                                && ny < h as isize
+                                && map[ny as usize][nx as usize] == Cell::Empty
+                                && dist[ny as usize][nx as usize]
+                                    >= dist[y as usize][x] + min_saving + 2
+                        })
+                        .count()
+                    } else {
+                        0
+                    }
+                })
+                .sum::<usize>()
+        })
+        .sum()
+}
+
+#[aoc(day20, part2)]
+fn part2(input: &Input) -> usize {
+    let start = input.0;
+    let end = input.1;
+    let map = &input.2;
+
+    #[cfg(not(test))]
+    let min_saving = 100;
+    #[cfg(test)]
+    let min_saving = 60;
+
+    let max_skip = 20;
+
+    let w = map[0].len();
+    let h = map.len();
+
+    let mut dist = vec![vec![usize::MAX; w]; h];
+    dist[start.1][start.0] = 0;
+
+    let mut deque = std::collections::VecDeque::new();
+    deque.push_back((0, start));
+
+    while let Some((d, pos)) = deque.pop_front() {
+        if dist[pos.1][pos.0] < d {
+            continue;
+        }
+
+        dist[pos.1][pos.0] = d;
+
+        [(1, 0), (-1, 0), (0, -1), (0, 1)]
+            .iter()
+            .for_each(|(dx, dy)| {
+                let x = (pos.0 as isize + dx) as usize;
+                let y = (pos.1 as isize + dy) as usize;
+
+                if x < w && y < h && map[y][x] == Cell::Empty {
+                    let new_d = d + 1;
+                    if new_d < dist[y][x] {
+                        deque.push_back((new_d, (x, y)));
+                    }
+                }
+            })
+    }
+
+    map.iter()
+        .enumerate()
+        .map(|(y, line)| {
+            line.iter()
+                .enumerate()
+                .map(|(x, cell)| {
+                    let y = y as isize;
+                    if *cell == Cell::Empty {
+                        (-max_skip..=max_skip)
+                            .flat_map(|dx: isize| {
+                                let skip = max_skip - dx.abs();
+                                (-skip..=skip).map(move |dy| (dx, dy))
+                            })
+                            .filter(|(dx, dy)| {
+                                let nx = x as isize + dx;
+                                let ny = y + dy;
+                                nx >= 0
+                                    && nx < w as isize
+                                    && ny >= 0
+                                    && ny < h as isize
+                                    && map[ny as usize][nx as usize] == Cell::Empty
+                                    && dist[ny as usize][nx as usize]
+                                        >= dist[y as usize][x]
+                                            + min_saving
+                                            + dx.unsigned_abs()
+                                            + dy.unsigned_abs()
+                            })
+                            .count()
+                    } else {
+                        0
+                    }
+                })
+                .sum::<usize>()
+        })
+        .sum()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn part1_example() {
+        assert_eq!(
+            part1(&parse(
+                "###############
+#...#...#.....#
+#.#.#.#.#.###.#
+#S#...#.#.#...#
+#######.#.#.###
+#######.#.#...#
+#######.#.###.#
+###..E#...#...#
+###.#######.###
+#...###...#...#
+#.#####.#.###.#
+#.#...#.#.#...#
+#.#.#.#.#.#.###
+#...#...#...###
+###############"
+            )),
+            44
+        );
+    }
+
+    #[test]
+    fn part2_example() {
+        assert_eq!(
+            part2(&parse(
+                "###############
+#...#...#.....#
+#.#.#.#.#.###.#
+#S#...#.#.#...#
+#######.#.#.###
+#######.#.#...#
+#######.#.###.#
+###..E#...#...#
+###.#######.###
+#...###...#...#
+#.#####.#.###.#
+#.#...#.#.#...#
+#.#.#.#.#.#.###
+#...#...#...###
+###############"
+            )),
+            129
+        );
+    }
+}

aoc_2024/src/day21.rs

@@ -0,0 +1,300 @@
+use std::iter::once;
+
+use aoc_runner_derive::{aoc, aoc_generator};
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+struct Path<T> {
+    steps: usize,
+    path: [Option<T>; 6],
+}
+
+impl<T: Copy> Path<T> {
+    fn new() -> Self {
+        Self {
+            steps: 0,
+            path: [None, None, None, None, None, None],
+        }
+    }
+
+    fn push(&mut self, button: T) {
+        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());
+        }
+    }
+}
+
+impl<T> IntoIterator for Path<T> {
+    type Item = T;
+    type IntoIter = std::iter::Flatten<std::array::IntoIter<Option<T>, 6>>;
+
+    fn into_iter(self) -> Self::IntoIter {
+        self.path.into_iter().flatten()
+    }
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+enum Button {
+    Num(NumButton),
+    Dir(DirButton),
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+enum DirButton {
+    Up,
+    Down,
+    Left,
+    Right,
+    A,
+}
+
+impl DirButton {
+    fn pos(&self) -> (usize, usize) {
+        match self {
+            DirButton::Up => (1, 0),
+            DirButton::Down => (1, 1),
+            DirButton::Left => (0, 1),
+            DirButton::Right => (2, 1),
+            DirButton::A => (2, 0),
+        }
+    }
+
+    fn index(&self) -> usize {
+        match self {
+            DirButton::Up => 0,
+            DirButton::Down => 1,
+            DirButton::Left => 2,
+            DirButton::Right => 3,
+            DirButton::A => 4,
+        }
+    }
+
+    fn to(&self, other: &DirButton) -> [Option<Path<DirButton>>; 2] {
+        let start = self.pos();
+        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)]
+enum NumButton {
+    One,
+    Two,
+    Three,
+    Four,
+    Five,
+    Six,
+    Seven,
+    Eight,
+    Nine,
+    Zero,
+    A,
+}
+
+impl NumButton {
+    fn pos(&self) -> (usize, usize) {
+        match self {
+            NumButton::One => (0, 2),
+            NumButton::Two => (1, 2),
+            NumButton::Three => (2, 2),
+            NumButton::Four => (0, 1),
+            NumButton::Five => (1, 1),
+            NumButton::Six => (2, 1),
+            NumButton::Seven => (0, 0),
+            NumButton::Eight => (1, 0),
+            NumButton::Nine => (2, 0),
+            NumButton::Zero => (1, 3),
+            NumButton::A => (2, 3),
+        }
+    }
+
+    fn to(&self, other: &NumButton) -> [Option<Path<DirButton>>; 2] {
+        let start = self.pos();
+        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 == 3 {
+            x.append(&y);
+            x.push(DirButton::A);
+            [Some(x), None]
+        } else if end.0 == 0 && start.1 == 3 {
+            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)]
+        }
+    }
+}
+
+type Input = Vec<(usize, Vec<NumButton>)>;
+
+#[aoc_generator(day21)]
+fn parse(input: &str) -> Input {
+    input
+        .lines()
+        .map(|line| {
+            (
+                line[0..3].parse().unwrap(),
+                line.chars()
+                    .map(|c| match c {
+                        '1' => NumButton::One,
+                        '2' => NumButton::Two,
+                        '3' => NumButton::Three,
+                        '4' => NumButton::Four,
+                        '5' => NumButton::Five,
+                        '6' => NumButton::Six,
+                        '7' => NumButton::Seven,
+                        '8' => NumButton::Eight,
+                        '9' => NumButton::Nine,
+                        '0' => NumButton::Zero,
+                        'A' => NumButton::A,
+                        _ => unreachable!(),
+                    })
+                    .collect(),
+            )
+        })
+        .collect()
+}
+
+type DistanceMatrix = [[usize; 5]; 5];
+
+fn calculate_steps(start: DirButton, end: DirButton, steps: &mut [DistanceMatrix]) -> usize {
+    if steps.is_empty() {
+        return 1;
+    }
+
+    if steps[0][start.index()][end.index()] == 0 {
+        let extension = start
+            .to(&end)
+            .into_iter()
+            .flatten()
+            .map(|path| shortest_dir_path(path, &mut steps[1..]))
+            .min()
+            .unwrap();
+        steps[0][start.index()][end.index()] = extension;
+    }
+
+    steps[0][start.index()][end.index()]
+}
+
+fn shortest_dir_path(path: Path<DirButton>, steps: &mut [DistanceMatrix]) -> usize {
+    path.path
+        .into_iter()
+        .flatten()
+        .fold((0, DirButton::A), |acc, next| {
+            let sum = acc.0;
+            let pos = acc.1;
+
+            let extension = calculate_steps(pos, next, steps);
+
+            (sum + extension, next)
+        })
+        .0
+}
+
+fn shortest_path(path: Vec<NumButton>, steps: &mut [DistanceMatrix]) -> usize {
+    path.into_iter()
+        .fold((0, NumButton::A), |acc, end| {
+            let sum = acc.0;
+            let start = acc.1;
+
+            let extension = start
+                .to(&end)
+                .into_iter()
+                .flatten()
+                .map(|path| shortest_dir_path(path, steps))
+                .min()
+                .unwrap();
+            (sum + extension, end)
+        })
+        .0
+}
+
+#[aoc(day21, part1)]
+fn part1(input: &Input) -> usize {
+    let mut steps = vec![[[0; 5]; 5]; 3 - 1];
+
+    input
+        .iter()
+        .cloned()
+        .map(|(num, path)| num * shortest_path(path, &mut steps))
+        .sum()
+}
+
+#[aoc(day21, part2)]
+fn part2(input: &Input) -> usize {
+    let mut steps = vec![[[0; 5]; 5]; 26 - 1];
+
+    input
+        .iter()
+        .cloned()
+        .map(|(num, path)| num * shortest_path(path, &mut steps))
+        .sum()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn part1_example() {
+        assert_eq!(part1(&parse("179A")), 68 * 179);
+        assert_eq!(part1(&parse("379A")), 64 * 379);
+        assert_eq!(part1(&parse("456A")), 64 * 456);
+        assert_eq!(part1(&parse("980A")), 60 * 980);
+        assert_eq!(part1(&parse("029A")), 68 * 29);
+    }
+}

aoc_2024/src/lib.rs

@@ -1,6 +1,4 @@
-mod day19;
-mod day18;
-mod day17;
+mod day21;
 mod day1;
 mod day10;
 mod day11;
@@ -9,7 +7,11 @@ mod day13;
 mod day14;
 mod day15;
 mod day16;
+mod day17;
+mod day18;
+mod day19;
 mod day2;
+mod day20;
 mod day3;
 mod day4;
 mod day5;