Year 2024, Day 15, part 1

year2024/src/day15.rs

@@ -0,0 +1,149 @@
+use common::day::Day;
+use util::grid2d::{Coords, Direction, Grid2D};
+
+pub struct Day15 {}
+
+impl Day for Day15 {
+    fn star1(&self, input: &str) -> String {
+        let (mut grid, dirs) = parse_input(input);
+        let mut cur_pos = grid.find(Field::Robot).unwrap();
+        for dir in dirs {
+            cur_pos = move_robot(&mut grid, cur_pos, dir);
+        }
+        gps_sum(&grid).to_string()
+    }
+
+    fn star2(&self, _input: &str) -> String {
+        String::from("not implemented")
+    }
+}
+
+#[derive(PartialEq, Eq)]
+enum Field {
+    Robot,
+    Box,
+    Wall,
+    Empty,
+}
+
+fn parse_input(input: &str) -> (Grid2D<Field>, Vec<Direction>) {
+    let mut secs = input.split("\n\n");
+    let grid = Grid2D::new_by(secs.next().unwrap(), |c| match c {
+        '@' => Field::Robot,
+        'O' => Field::Box,
+        '#' => Field::Wall,
+        '.' => Field::Empty,
+        _ => unreachable!(),
+    })
+    .unwrap();
+
+    let dirs = secs
+        .next()
+        .unwrap()
+        .chars()
+        .flat_map(|c| match c {
+            '^' => Some(Direction::N),
+            '>' => Some(Direction::E),
+            'v' => Some(Direction::S),
+            '<' => Some(Direction::W),
+            '\n' => None,
+            _ => {
+                unreachable!()
+            }
+        })
+        .collect();
+
+    (grid, dirs)
+}
+
+fn move_robot(grid: &mut Grid2D<Field>, mut cur_pos: Coords, dir: Direction) -> Coords {
+    let new_pos = cur_pos.mov(dir);
+    match grid.at(&new_pos).unwrap() {
+        Field::Robot => unreachable!(),
+        Field::Box => {
+            let mut shift_pos = new_pos.mov(dir);
+            let can_move = loop {
+                match grid.at(&shift_pos).unwrap() {
+                    Field::Robot => unreachable!(),
+                    Field::Box => {}
+                    Field::Wall => {
+                        break false;
+                    }
+                    Field::Empty => {
+                        break true;
+                    }
+                }
+                shift_pos = shift_pos.mov(dir);
+            };
+
+            if can_move {
+                grid.set(&shift_pos, Field::Box);
+                grid.set(&new_pos, Field::Robot);
+                grid.set(&cur_pos, Field::Empty);
+                cur_pos = new_pos;
+            }
+        }
+        Field::Wall => {
+            // cannot move
+        }
+        Field::Empty => {
+            grid.set(&new_pos, Field::Robot);
+            grid.set(&cur_pos, Field::Empty);
+            cur_pos = new_pos;
+        }
+    }
+
+    cur_pos
+}
+
+fn gps_sum(grid: &Grid2D<Field>) -> i64 {
+    grid.filter(&[Field::Box])
+        .iter()
+        .map(|c| c.x + 100 * c.y)
+        .sum()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const INPUT1: &str = r#"########
+#..O.O.#
+##@.O..#
+#...O..#
+#.#.O..#
+#...O..#
+#......#
+########
+
+<^^>>>vv<v>>v<<"#;
+
+    const INPUT2: &str = 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^<<^"#;
+
+    #[test]
+    fn star1() {
+        let d = Day15 {};
+        assert_eq!(d.star1(INPUT1), "2028");
+        assert_eq!(d.star1(INPUT2), "10092");
+    }
+}

year2024/src/lib.rs

@@ -15,6 +15,7 @@ mod day11;
 mod day12;
 mod day13;
 mod day14;
+mod day15;
 
 pub struct Year2024 {}
 
@@ -35,6 +36,7 @@ impl Year for Year2024 {
             12 => Some(Box::new(day12::Day12 {})),
             13 => Some(Box::new(day13::Day13 {})),
             14 => Some(Box::new(day14::Day14 {})),
+            15 => Some(Box::new(day15::Day15 {})),
             _ => None,
         }
     }