From dc5f48821202b3890ecadd80c3b08d0efb54c1b7 Mon Sep 17 00:00:00 2001
From: Jan-Bulthuis <git@bulthuis.dev>
Date: Mon, 16 Dec 2024 17:44:55 +0100
Subject: [PATCH] day16

---
 aoc_2024/src/day16.rs | 287 ++++++++++++++++++++++++++++++++++++++++++
 aoc_2024/src/lib.rs   |   1 +
 2 files changed, 288 insertions(+)
 create mode 100644 aoc_2024/src/day16.rs

diff --git a/aoc_2024/src/day16.rs b/aoc_2024/src/day16.rs
new file mode 100644
index 0000000..5bf475a
--- /dev/null
+++ b/aoc_2024/src/day16.rs
@@ -0,0 +1,287 @@
+use std::{
+    cmp::{Ordering, Reverse},
+    collections::BinaryHeap,
+};
+
+use aoc_runner_derive::{aoc, aoc_generator};
+use hashbrown::HashSet;
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+enum Cell {
+    Empty,
+    Wall,
+}
+
+type Input = ((usize, usize), (usize, usize), Vec<Vec<Cell>>);
+
+#[aoc_generator(day16)]
+fn parse(input: &str) -> Input {
+    let mut pos = (0, 0);
+    let mut end = (0, 0);
+    let map = input
+        .lines()
+        .enumerate()
+        .map(|(y, line)| {
+            line.chars()
+                .enumerate()
+                .map(|(x, c)| match c {
+                    '#' => Cell::Wall,
+                    '.' => Cell::Empty,
+                    'E' => {
+                        end = (x, y);
+                        Cell::Empty
+                    }
+                    'S' => {
+                        pos = (x, y);
+                        Cell::Empty
+                    }
+                    _ => unreachable!(),
+                })
+                .collect()
+        })
+        .collect();
+    (pos, end, map)
+}
+
+#[aoc(day16, part1)]
+fn part1(input: &Input) -> i64 {
+    let start = (input.0 .0 as i64, input.0 .1 as i64);
+    let end = (input.1 .0 as i64, input.1 .1 as i64);
+    let map = input.2.clone();
+    let w = map[0].len();
+    let h = map.len();
+    let mut d = vec![vec![[i64::MAX; 4]; w]; h];
+
+    #[allow(clippy::type_complexity)]
+    let mut queue: BinaryHeap<Reverse<(i64, i64, i64, i64, i64)>> = BinaryHeap::new();
+    d[start.1 as usize][start.0 as usize][1] = 0;
+    queue.push(Reverse((0, start.0, start.1, 1, 0)));
+
+    while let Some(Reverse((dist, pos_x, pos_y, dir_x, dir_y))) = queue.pop() {
+        let dir_num = match (dir_x, dir_y) {
+            (0, -1) => 0,
+            (1, 0) => 1,
+            (0, 1) => 2,
+            (-1, 0) => 3,
+            _ => unreachable!(),
+        };
+
+        if d[pos_y as usize][pos_x as usize][dir_num] < dist {
+            continue;
+        }
+
+        if (pos_x, pos_y) == end {
+            break;
+        }
+
+        if map[(pos_y + dir_y) as usize][(pos_x + dir_x) as usize] == Cell::Empty {
+            let dist_next = &mut d[(pos_y + dir_y) as usize][(pos_x + dir_x) as usize][dir_num];
+            if (dist + 1).cmp(dist_next) == Ordering::Less {
+                *dist_next = dist + 1;
+                queue.push(Reverse((
+                    *dist_next,
+                    pos_x + dir_x,
+                    pos_y + dir_y,
+                    dir_x,
+                    dir_y,
+                )));
+            }
+        }
+
+        {
+            let dist_next = &mut d[pos_y as usize][pos_x as usize][(dir_num + 3) % 4];
+            if (dist + 1000).cmp(dist_next) == Ordering::Less {
+                *dist_next = dist + 1000;
+                queue.push(Reverse((*dist_next, pos_x, pos_y, dir_y, -dir_x)));
+            }
+        }
+
+        {
+            let dist_next = &mut d[pos_y as usize][pos_x as usize][(dir_num + 1) % 4];
+            if (dist + 1000).cmp(dist_next) == Ordering::Less {
+                *dist_next = dist + 1000;
+                queue.push(Reverse((*dist_next, pos_x, pos_y, -dir_y, dir_x)));
+            }
+        }
+    }
+
+    *d[end.1 as usize][end.0 as usize].iter().min().unwrap()
+}
+
+#[aoc(day16, part2)]
+fn part2(input: &Input) -> i64 {
+    let start = (input.0 .0 as i64, input.0 .1 as i64);
+    let end = (input.1 .0 as i64, input.1 .1 as i64);
+    let map = input.2.clone();
+    let w = map[0].len();
+    let h = map.len();
+    let mut d = vec![vec![[i64::MAX; 4]; w]; h];
+    let mut b = vec![vec![[vec![], vec![], vec![], vec![]]; w]; h];
+
+    #[allow(clippy::type_complexity)]
+    let mut queue: BinaryHeap<Reverse<(i64, i64, i64, i64, i64)>> = BinaryHeap::new();
+    d[start.1 as usize][start.0 as usize][1] = 0;
+    queue.push(Reverse((0, start.0, start.1, 1, 0)));
+
+    while let Some(Reverse((dist, pos_x, pos_y, dir_x, dir_y))) = queue.pop() {
+        let dir_num = match (dir_x, dir_y) {
+            (0, -1) => 0,
+            (1, 0) => 1,
+            (0, 1) => 2,
+            (-1, 0) => 3,
+            _ => unreachable!(),
+        };
+
+        if d[pos_y as usize][pos_x as usize][dir_num] < dist {
+            continue;
+        }
+
+        if (pos_x, pos_y) == end {
+            break;
+        }
+
+        if map[(pos_y + dir_y) as usize][(pos_x + dir_x) as usize] == Cell::Empty {
+            let dist_next = &mut d[(pos_y + dir_y) as usize][(pos_x + dir_x) as usize][dir_num];
+            let back_next = &mut b[(pos_y + dir_y) as usize][(pos_x + dir_x) as usize][dir_num];
+            if (dist + 1).cmp(dist_next) == Ordering::Less {
+                *dist_next = dist + 1;
+                back_next.clear();
+                back_next.push((pos_x, pos_y, dir_num));
+                queue.push(Reverse((
+                    *dist_next,
+                    pos_x + dir_x,
+                    pos_y + dir_y,
+                    dir_x,
+                    dir_y,
+                )));
+            } else if (dist + 1).cmp(dist_next) == Ordering::Equal {
+                back_next.push((pos_x, pos_y, dir_num));
+            }
+        }
+
+        {
+            let dist_next = &mut d[pos_y as usize][pos_x as usize][(dir_num + 3) % 4];
+            let back_next = &mut b[pos_y as usize][pos_x as usize][(dir_num + 3) % 4];
+            if (dist + 1000).cmp(dist_next) == Ordering::Less {
+                *dist_next = dist + 1000;
+                back_next.clear();
+                back_next.push((pos_x, pos_y, dir_num));
+                queue.push(Reverse((*dist_next, pos_x, pos_y, dir_y, -dir_x)));
+            } else if (dist + 1000).cmp(dist_next) == Ordering::Equal {
+                back_next.push((pos_x, pos_y, dir_num));
+            }
+        }
+
+        {
+            let dist_next = &mut d[pos_y as usize][pos_x as usize][(dir_num + 1) % 4];
+            let back_next = &mut b[pos_y as usize][pos_x as usize][(dir_num + 1) % 4];
+            if (dist + 1000).cmp(dist_next) == Ordering::Less {
+                *dist_next = dist + 1000;
+                back_next.clear();
+                back_next.push((pos_x, pos_y, dir_num));
+                queue.push(Reverse((*dist_next, pos_x, pos_y, -dir_y, dir_x)));
+            } else if (dist + 1000).cmp(dist_next) == Ordering::Equal {
+                back_next.push((pos_x, pos_y, dir_num));
+            }
+        }
+    }
+
+    let mut visited = HashSet::new();
+    let dist_min = *d[end.1 as usize][end.0 as usize].iter().min().unwrap();
+    let mut stack = vec![];
+    d[end.1 as usize][end.0 as usize]
+        .iter()
+        .enumerate()
+        .for_each(|(i, d)| {
+            if *d == dist_min {
+                stack.push((end.0, end.1, i));
+            }
+        });
+
+    while let Some((pos_x, pos_y, dir_num)) = stack.pop() {
+        visited.insert((pos_x, pos_y));
+        stack.append(&mut b[pos_y as usize][pos_x as usize][dir_num]);
+    }
+
+    visited.len() as i64
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn part1_example() {
+        assert_eq!(
+            part1(&parse(
+                "###############
+#.......#....E#
+#.#.###.#.###.#
+#.....#.#...#.#
+#.###.#####.#.#
+#.#.#.......#.#
+#.#.#####.###.#
+#...........#.#
+###.#.#####.#.#
+#...#.....#.#.#
+#.#.#.###.#.#.#
+#.....#...#.#.#
+#.###.#.#.#.#.#
+#S..#.....#...#
+###############"
+            )),
+            7036
+        );
+        assert_eq!(
+            part1(&parse(include_str!("../input/2024/day16.txt"))),
+            85420
+        );
+    }
+
+    #[test]
+    fn part2_example() {
+        assert_eq!(
+            part2(&parse(
+                "###############
+#.......#....E#
+#.#.###.#.###.#
+#.....#.#...#.#
+#.###.#####.#.#
+#.#.#.......#.#
+#.#.#####.###.#
+#...........#.#
+###.#.#####.#.#
+#...#.....#.#.#
+#.#.#.###.#.#.#
+#.....#...#.#.#
+#.###.#.#.#.#.#
+#S..#.....#...#
+###############"
+            )),
+            45
+        );
+        assert_eq!(
+            part2(&parse(
+                "#################
+#...#...#...#..E#
+#.#.#.#.#.#.#.#.#
+#.#.#.#...#...#.#
+#.#.#.#.###.#.#.#
+#...#.#.#.....#.#
+#.#.#.#.#.#####.#
+#.#...#.#.#.....#
+#.#.#####.#.###.#
+#.#.#.......#...#
+#.#.###.#####.###
+#.#.#...#.....#.#
+#.#.#.#####.###.#
+#.#.#.........#.#
+#.#.#.#########.#
+#S#.............#
+#################"
+            )),
+            64
+        );
+        assert_eq!(part2(&parse(include_str!("../input/2024/day16.txt"))), 492);
+    }
+}
diff --git a/aoc_2024/src/lib.rs b/aoc_2024/src/lib.rs
index 0e6b7ae..c53a429 100644
--- a/aoc_2024/src/lib.rs
+++ b/aoc_2024/src/lib.rs
@@ -5,6 +5,7 @@ mod day12;
 mod day13;
 mod day14;
 mod day15;
+mod day16;
 mod day2;
 mod day3;
 mod day4;