AOC 2024 Day 15 Part 1

Author: raul-sauco

aoc/2024/rust/data/examples/15.txt

@@ -0,0 +1,197 @@
+advent_of_code::solution!(15);
+
+use std::collections::HashMap;
+
+use glam::IVec2;
+
+#[derive(Debug, PartialEq)]
+enum Cell {
+    Wall,
+    Box,
+    Robot,
+    Empty,
+}
+
+impl Cell {
+    fn from_char(c: char) -> Self {
+        match c {
+            '#' => Cell::Wall,
+            'O' => Cell::Box,
+            '@' => Cell::Robot,
+            _ => Cell::Empty,
+        }
+    }
+}
+
+#[derive(Debug)]
+enum Dir {
+    N,
+    E,
+    S,
+    W,
+}
+
+impl Dir {
+    fn from_char(c: char) -> Self {
+        match c {
+            '^' => Self::N,
+            '>' => Self::E,
+            'v' => Self::S,
+            '<' => Self::W,
+            _ => panic!("Bad direction {c}"),
+        }
+    }
+}
+
+fn parse_grid(input: &str) -> HashMap<IVec2, Cell> {
+    input
+        .lines()
+        .enumerate()
+        .flat_map(|(y, line)| {
+            line.chars()
+                .enumerate()
+                .filter(|(_, c)| *c != '.')
+                .map(move |(x, c)| (IVec2::new(x as i32, y as i32), Cell::from_char(c)))
+        })
+        .collect::<HashMap<_, _>>()
+}
+
+fn parse_moves(input: &str) -> Vec<Dir> {
+    input
+        .chars()
+        .filter(|c| *c != '\n')
+        .map(Dir::from_char)
+        .collect()
+}
+
+fn parse_input(input: &str) -> (HashMap<IVec2, Cell>, Vec<Dir>) {
+    let mut sp = input.split("\n\n");
+    let grid = parse_grid(sp.next().unwrap());
+    let moves = parse_moves(sp.next().unwrap());
+    (grid, moves)
+}
+
+fn make_move(current_position: &IVec2, grid: &mut HashMap<IVec2, Cell>, dir: Dir) -> IVec2 {
+    let v = match dir {
+        Dir::N => IVec2::NEG_Y,
+        Dir::E => IVec2::X,
+        Dir::S => IVec2::Y,
+        Dir::W => IVec2::NEG_X,
+    };
+    if let Some(c) = grid.get(&(current_position + v)) {
+        match c {
+            Cell::Box => {
+                let first_box = current_position + v;
+                for i in 2..50 {
+                    let dest = current_position + v * i;
+                    match grid.get(&dest) {
+                        Some(dest_content) => {
+                            match dest_content {
+                                Cell::Wall => {
+                                    return *current_position;
+                                }
+                                Cell::Box => continue,
+                                _ => {
+                                    // We found an empty cell.
+                                    grid.insert(dest, Cell::Box);
+                                    grid.remove(&first_box);
+                                    return first_box;
+                                }
+                            }
+                        }
+                        None => {
+                            // We found an empty cell.
+                            grid.insert(dest, Cell::Box);
+                            grid.remove(&first_box);
+                            return first_box;
+                        }
+                    }
+                }
+            }
+            Cell::Wall => {
+                return *current_position;
+            }
+            _ => {
+                return current_position + v;
+            }
+        }
+    } else {
+        // The destination cell is free.
+        return current_position + v;
+    }
+    unreachable!("Should have returned next position")
+}
+
+pub fn part_one(input: &str) -> Option<u32> {
+    let (mut grid, moves) = parse_input(input);
+    let (start, _) = grid.iter().find(|(_, v)| **v == Cell::Robot).unwrap();
+    let mut current_position = *start;
+    grid.remove(&current_position);
+    for dir in moves {
+        current_position = make_move(&current_position, &mut grid, dir);
+    }
+    Some(
+        grid.iter()
+            .map(|(k, v)| if *v == Cell::Box { 100 * k.y + k.x } else { 0 })
+            .sum::<i32>() as _,
+    )
+}
+
+// TODO: Day 15 part 2
+pub fn part_two(_input: &str) -> Option<u32> {
+    None
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use test_case::test_case;
+
+    #[test_case(
+        r#"########
+#..O.O.#
+##@.O..#
+#...O..#
+#.#.O..#
+#...O..#
+#......#
+########
+
+<^^>>>vv<v>>v<<"#,
+        Some(2028); "Small grid"
+    )]
+    #[test_case(
+        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^<<^"#,
+        Some(10092); "Large grid"
+    )]
+    fn test_part_one(input: &str, expected: Option<u32>) {
+        let result = part_one(input);
+        assert_eq!(result, expected);
+    }
+
+    #[test]
+    fn test_part_two() {
+        let result = part_two(&advent_of_code::template::read_file("examples", DAY));
+        assert_eq!(result, None);
+    }
+}