day20

aoc_2024/src/day20.rs

@@ -0,0 +1,262 @@
+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
+                        })
+                        // .inspect(|v| {
+                        //     println!("{:?} {:?}", (x, y), v);
+                        // })
+                        .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()
+                            })
+                            // .inspect(|v| {
+                            //     println!("{:?} {:?}", (x, y), v);
+                            // })
+                            .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/lib.rs

@@ -1,6 +1,3 @@
-mod day19;
-mod day18;
-mod day17;
 mod day1;
 mod day10;
 mod day11;
@@ -9,7 +6,11 @@ mod day13;
 mod day14;
 mod day15;
 mod day16;
+mod day17;
+mod day18;
+mod day19;
 mod day2;
+mod day20;
 mod day3;
 mod day4;
 mod day5;