solve: day15

Author: tom-anders

Cargo.toml

@@ -2,7 +2,7 @@
 resolver = "2"
 members = [
     "utils",
-    "aoc_derive", "day1", "day2", "day3", "day4", "day5", "day6", "day7", "day8", "day9", "day10", "day11", "day12", "day13", "day14",
+    "aoc_derive", "day1", "day2", "day3", "day4", "day5", "day6", "day7", "day8", "day9", "day10", "day11", "day12", "day13", "day14", "day15",
 ]
 
 [workspace.dependencies]

day15/Cargo.toml

@@ -0,0 +1,18 @@
+[package]
+name = "day15"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
+aoc_derive.path = '../aoc_derive'
+utils.path = '../utils'
+derive_more.workspace = true
+itertools.workspace = true
+lazy-regex.workspace = true
+parse-display.workspace = true
+rayon.workspace = true
+regex.workspace = true
+num.workspace = true
+
+[dev-dependencies]
+pretty_assertions.workspace = true

day15/src/main.rs

@@ -0,0 +1,214 @@
+use aoc_derive::aoc_main;
+use grid::Grid;
+use itertools::Itertools;
+use math::Vec2D;
+use utils::*;
+
+fn try_move_part1(pos: Vec2D, heading: Vec2D, map: &mut Grid<char>) -> bool {
+    match map[pos] {
+        '.' => {
+            map.swap(pos, pos - heading);
+            true
+        }
+        '#' => false,
+        'O' => {
+            let can_move = try_move_part1(pos + heading, heading, map);
+            if can_move {
+                map.swap(pos, pos - heading);
+            }
+            can_move
+        }
+        _ => unreachable!(),
+    }
+}
+
+fn part1(mut map: Grid<char>, instructions: &str) -> i64 {
+    let mut pos = map.iter().find_map(|(pos, &c)| (c == '@').then_some(pos)).unwrap();
+    map[pos] = '.';
+
+    for heading in instructions.chars().filter(|c| !c.is_ascii_whitespace()).map(|instr| {
+        Vec2D::from(match instr {
+            'v' => (0, 1),
+            '>' => (1, 0),
+            '<' => (-1, 0),
+            '^' => (0, -1),
+            _ => unreachable!(),
+        })
+    }) {
+        if try_move_part1(pos + heading, heading, &mut map) {
+            pos += heading;
+        }
+    }
+
+    map.iter().filter_map(|(pos, &c)| (c == 'O').then_some(pos.x + 100 * pos.y)).sum()
+}
+
+fn try_move_horizontally_part2(pos: Vec2D, heading: Vec2D, map: &mut Grid<char>) -> bool {
+    if let Some(dot) = (1..)
+        .find_map(|i| match map[pos + i * heading] {
+            '.' => Some(Some(i)),
+            '#' => Some(None),
+            _ => None,
+        })
+        .unwrap()
+    {
+        for j in (0..dot).rev() {
+            map.swap(pos + (j + 1) * heading, pos + j * heading);
+        }
+        return true;
+    }
+    false
+}
+
+fn try_move_vertically_part2(pos: Vec2D, heading: Vec2D, map: &mut Grid<char>) -> bool {
+    match map[pos + heading] {
+        '#' => return false,
+        '.' => {
+            return true;
+        }
+        _ => (),
+    }
+
+    let mut to_move = vec![vec![
+        pos + heading,
+        pos + heading + if map[pos + heading] == ']' { (-1, 0) } else { (1, 0) },
+    ]];
+    loop {
+        let upper_row = to_move.last().unwrap();
+
+        if upper_row.iter().any(|&pos| map[pos + heading] == '#') {
+            // Can't move
+            return false;
+        }
+
+        if upper_row.iter().all(|&pos| map[pos + heading] == '.') {
+            for row in to_move.into_iter().rev() {
+                for pos in row {
+                    map.swap(pos + heading, pos);
+                }
+            }
+
+            return true;
+        }
+
+        to_move.push(
+            upper_row
+                .iter()
+                .flat_map(|&pos| match map[pos + heading] {
+                    ']' => vec![pos + heading, pos + heading + (-1, 0)],
+                    '[' => vec![pos + heading, pos + heading + (1, 0)],
+                    _ => vec![],
+                })
+                .unique()
+                .collect(),
+        );
+    }
+}
+
+fn part2(map: &str, instructions: &str) -> i64 {
+    let mut map = map
+        .trim()
+        .lines()
+        .map(|line| {
+            line.chars().flat_map(|c| {
+                match c {
+                    '#' => "##",
+                    'O' => "[]",
+                    '.' => "..",
+                    '@' => "@.",
+                    _ => unreachable!(),
+                }
+                .chars()
+            })
+        })
+        .collect::<Grid<char>>();
+
+    let mut pos = map.iter().find_map(|(pos, &c)| (c == '@').then_some(pos)).unwrap();
+    map[pos] = '.';
+
+    for heading in instructions.chars().filter(|c| !c.is_ascii_whitespace()).map(|instr| {
+        Vec2D::from(match instr {
+            'v' => (0, 1),
+            '>' => (1, 0),
+            '<' => (-1, 0),
+            '^' => (0, -1),
+            _ => unreachable!(),
+        })
+    }) {
+        if heading.y == 0 && try_move_horizontally_part2(pos, heading, &mut map)
+            || try_move_vertically_part2(pos, heading, &mut map)
+        {
+            pos += heading
+        }
+    }
+
+    map.iter().filter_map(|(pos, &c)| (c == '[').then_some(pos.x + 100 * pos.y)).sum()
+}
+
+#[aoc_main]
+fn solve(input: Input) -> impl Into<Solution> {
+    let (map, instructions) = input.blocks().collect_tuple().unwrap();
+
+    (part1(map.lines().map(str::chars).collect(), instructions), part2(map, instructions))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    #[test]
+    fn test_examples() {
+        part2(
+            "
+#######
+#...#.#
+#.....#
+#..OO@#
+#..O..#
+#.....#
+#######",
+            "<vv<<^^<<^^",
+        );
+
+        assert_example!(
+            "
+########
+#..O.O.#
+##@.O..#
+#...O..#
+#.#.O..#
+#...O..#
+#......#
+########
+
+<^^>>>vv<v>>v<<
+            ",
+            2028
+        );
+
+        assert_example!(
+            r"##########
+#..O..O.O#
+#......O.#
+#.OO..O.O#
+#[email protected].#
+#O#..O...#
+#O..O..O.#
+#.OO.O.OO#
+#....O...#
+##########
+
+<vv>^<v^>v>^vv^v>v<>v^v<v<^vv<<<^><<><>>v<vvv<>^v^>^<<<><<v<<<v^vv^v>^
+vvv<<^>^v^^><<>>><>^<<><^vv^^<>vvv<>><^^v>^>vv<>v<<<<v<^v>^<^^>>>^<v<v
+><>vv>v^v^<>><>>>><^^>vv>v<^^^>>v^v^<^^>v^^>v^<^v>v<>>v^v^<v>v^^<^^vv<
+<<v<^>>^^^^>>>v^<>vvv^><v<<<>^^^vv^<vvv>^>v<^^^^v<>^>vvvv><>>v^<<^^^^^
+^><^><>>><>^^<<^^v>>><^<v>^<vv>>v>>>^v><>^v><<<<v>>v<v<v>vvv>^<><<>^><
+^>><>^v<><^vvv<^^<><v<<<<<><^v<<<><<<^^<v<^^^><^>>^<v^><<<^>>^v<v^v<v^
+>^>>^v>vv>^<<^v<>><<><<v<<v><>v<^vv<<<>^^v^>^^>>><<^v>>v^v><^^>>^<>vv^
+<><^^>^^^<><vvvvv^v<v<<>^v<v>v<<^><<><<><<<^^<<<^<<>><<><^^^>^^<>^>v<>
+^^>vv<^v^v<vv>^<><v<^v>^^^>>>^^vvv^>vvv<>>>^<^>>>>>^<<^v>^vvv<>^<><<v>
+v^^>>><<^^<>>^v^<v^vv<>v^<<>^<^v^v><^<<<><<^<v><v<>vv>>v><v^<vv<>v^<<^",
+            10092,
+            9021
+        );
+    }
+}