From: Greg Burri <greg.burri@gmail.com>
Date: Mon, 16 Dec 2024 21:55:22 +0000 (+0100)
Subject: Day 15
X-Git-Url: https://git.euphorik.ch/?a=commitdiff_plain;h=refs%2Fheads%2Fmaster;p=advent_of_code_2024.git

Day 15
---

diff --git a/src/day14.rs b/src/day14.rs
index 5d422ba..9f3296b 100644
--- a/src/day14.rs
+++ b/src/day14.rs
@@ -7,7 +7,7 @@ type Position = Point2<i64>;
 type Velocity = Vector2<i64>;
 
 pub fn read(reader: &mut dyn BufRead) -> Vec<(Position, Velocity)> {
-    let regex_line = { Regex::new(r#"([+-]?\d+),([+-]?\d+).*?([+-]?\d+),([+-]?\d+)"#).unwrap() };
+    let regex_line = Regex::new(r#"([+-]?\d+),([+-]?\d+).*?([+-]?\d+),([+-]?\d+)"#).unwrap();
 
     reader
         .lines()
diff --git a/src/day15.rs b/src/day15.rs
new file mode 100644
index 0000000..5e133fb
--- /dev/null
+++ b/src/day15.rs
@@ -0,0 +1,216 @@
+use std::io::BufRead;
+
+use nalgebra::{DMatrix, Point2, Vector2};
+
+type Map = DMatrix<char>;
+type Pos = Point2<i32>;
+type Dir = Vector2<i32>;
+type Movements = Vec<Dir>;
+
+pub fn read(reader: &mut dyn BufRead) -> (Pos, Map, Movements) {
+    let mut robot_pos = Pos::default();
+    let mut data: Vec<char> = Vec::new();
+    let mut nb_rows = 0;
+
+    let mut lines_iter = reader.lines();
+
+    for (i, l) in lines_iter.by_ref().enumerate() {
+        let l = l.unwrap();
+        if l.is_empty() {
+            break;
+        }
+        nb_rows += 1;
+        for (j, c) in l.chars().enumerate() {
+            if c == '@' {
+                robot_pos = Pos::new(i as i32, j as i32);
+                data.push('.');
+            } else {
+                data.push(c);
+            }
+        }
+    }
+
+    let mut movements = Movements::new();
+
+    for l in lines_iter {
+        for c in l.unwrap().chars() {
+            movements.push(match c {
+                '>' => Dir::new(0, 1),
+                '<' => Dir::new(0, -1),
+                'v' => Dir::new(1, 0),
+                '^' => Dir::new(-1, 0),
+                _ => panic!("Uknown movement: {}", c),
+            });
+        }
+    }
+
+    (
+        robot_pos,
+        Map::from_row_slice(nb_rows, data.len() / nb_rows, &data),
+        movements,
+    )
+}
+
+pub fn gps_coordinates_sum(
+    mut pos: Pos,
+    mut map: Map,
+    movements: &Movements,
+    enlarge_map: bool,
+) -> usize {
+    fn can_push(map: &Map, pos: Pos, dir: Dir, other_side: bool) -> bool {
+        let c = map[(pos.x as usize, pos.y as usize)];
+        if c == '.' {
+            return true;
+        }
+        if c != '#' {
+            let pos_next = pos + dir;
+            if if dir.x == 0 || c == 'O' {
+                can_push(map, pos_next, dir, false)
+            } else {
+                let nearby = if c == '[' {
+                    pos + Dir::new(0, 1)
+                } else {
+                    pos + Dir::new(0, -1)
+                };
+                can_push(map, pos_next, dir, false)
+                    && (other_side || can_push(map, nearby, dir, true))
+            } {
+                return true;
+            }
+        }
+        false
+    }
+
+    fn push(map: &mut Map, pos: Pos, dir: Dir, other_side: bool) {
+        let c = map[(pos.x as usize, pos.y as usize)];
+        if c != '#' && c != '.' {
+            let pos_next = pos + dir;
+            if dir.x == 0 || c == 'O' {
+                push(map, pos_next, dir, false)
+            } else {
+                let nearby = if c == '[' {
+                    pos + Dir::new(0, 1)
+                } else {
+                    pos + Dir::new(0, -1)
+                };
+                push(map, pos_next, dir, false);
+                if !other_side {
+                    push(map, nearby, dir, true);
+                }
+            }
+            map[(pos_next.x as usize, pos_next.y as usize)] = map[(pos.x as usize, pos.y as usize)];
+            map[(pos.x as usize, pos.y as usize)] = '.';
+        }
+    }
+
+    fn enlarge(map: Map) -> Map {
+        let mut new_map = Map::repeat(map.nrows(), 2 * map.ncols(), '.');
+        for j in 0..map.ncols() {
+            for i in 0..map.nrows() {
+                if map[(i, j)] == 'O' {
+                    new_map[(i, 2 * j)] = '[';
+                    new_map[(i, 2 * j + 1)] = ']';
+                } else {
+                    new_map[(i, 2 * j)] = map[(i, j)];
+                    new_map[(i, 2 * j + 1)] = map[(i, j)];
+                }
+            }
+        }
+        new_map
+    }
+
+    if enlarge_map {
+        map = enlarge(map);
+        pos = Pos::new(pos.x, pos.y * 2);
+    }
+
+    for m in movements {
+        if can_push(&map, pos + m, *m, false) {
+            push(&mut map, pos + m, *m, false);
+            pos += m;
+        }
+    }
+
+    let mut gps_sum = 0;
+    for j in 0..map.ncols() {
+        for i in 0..map.nrows() {
+            let c = map[(i, j)];
+            if c == '[' || c == 'O' {
+                gps_sum += 100 * i + j;
+            }
+        }
+    }
+    gps_sum
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    static MAP_AND_MOVEMENTS_A: &str = "########
+#..O.O.#
+##@.O..#
+#...O..#
+#.#.O..#
+#...O..#
+#......#
+########
+
+<^^>>>vv<v>>v<<";
+
+    static MAP_AND_MOVEMENTS_B: &str = "##########
+#..O..O.O#
+#......O.#
+#.OO..O.O#
+#..O@..O.#
+#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 part1_a() {
+        let (pos, map, movements) = read(&mut MAP_AND_MOVEMENTS_A.as_bytes());
+        assert_eq!(gps_coordinates_sum(pos, map, &movements, false), 2028);
+    }
+
+    #[test]
+    fn part1_b() {
+        let (pos, map, movements) = read(&mut MAP_AND_MOVEMENTS_B.as_bytes());
+        assert_eq!(gps_coordinates_sum(pos, map, &movements, false), 10092);
+    }
+
+    static MAP_AND_MOVEMENTS_C: &str = "#######
+#...#.#
+#.....#
+#..OO@#
+#..O..#
+#.....#
+#######
+
+<vv<<^^<<^^";
+
+    #[test]
+    fn part2_c() {
+        let (pos, map, movements) = read(&mut MAP_AND_MOVEMENTS_C.as_bytes());
+        assert_eq!(gps_coordinates_sum(pos, map, &movements, true), 618);
+    }
+
+    #[test]
+    fn part2_b() {
+        let (pos, map, movements) = read(&mut MAP_AND_MOVEMENTS_B.as_bytes());
+        assert_eq!(gps_coordinates_sum(pos, map, &movements, true), 9021);
+    }
+}
diff --git a/src/days.rs b/src/days.rs
index 2932a11..3635b3d 100644
--- a/src/days.rs
+++ b/src/days.rs
@@ -134,3 +134,12 @@ pub fn day14(reader: &mut dyn BufRead) -> String {
         day14::format_robots(&robots, (101, 103), 7520)
     )
 }
+
+pub fn day15(reader: &mut dyn BufRead) -> String {
+    let (pos, map, movements) = day15::read(reader);
+    format!(
+        "part1: {}, part2: {}",
+        day15::gps_coordinates_sum(pos, map.clone(), &movements, false),
+        day15::gps_coordinates_sum(pos, map, &movements, true),
+    )
+}
diff --git a/src/main.rs b/src/main.rs
index e7d4c43..fefa9ec 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -16,7 +16,7 @@ mod day11;
 mod day12;
 mod day13;
 mod day14;
-// mod day15;
+mod day15;
 // mod day16;
 // mod day17;
 // mod day18;
@@ -47,7 +47,7 @@ fn main() {
         days::day12,
         days::day13,
         days::day14,
-        // days::day15,
+        days::day15,
         // days::day16,
         // days::day17,
         // days::day18,