Day 16: Reindeer Maze

README.md

@@ -20,5 +20,5 @@ Development occurs in language-specific directories:
 |[Day13.hs](hs/src/Day13.hs)|[Day13.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day13.kt)|[day13.py](py/aoc2024/day13.py)|[day13.rs](rs/src/day13.rs)|
 |[Day14.hs](hs/src/Day14.hs)|[Day14.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day14.kt)|[day14.py](py/aoc2024/day14.py)|[day14.rs](rs/src/day14.rs)|
 |[Day15.hs](hs/src/Day15.hs)|[Day15.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day15.kt)|[day15.py](py/aoc2024/day15.py)|[day15.rs](rs/src/day15.rs)|
-|[Day16.hs](hs/src/Day16.hs)|[Day16.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day16.kt)|[day16.py](py/aoc2024/day16.py)||
+|[Day16.hs](hs/src/Day16.hs)|[Day16.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day16.kt)|[day16.py](py/aoc2024/day16.py)|[day16.rs](rs/src/day16.rs)|
 |[Day17.hs](hs/src/Day17.hs)|[Day17.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day17.kt)|||

rs/benches/criterion.rs

@@ -1,5 +1,6 @@
 use aoc2024::{
-    day1, day10, day11, day12, day13, day14, day15, day2, day3, day4, day5, day6, day7, day8, day9,
+    day1, day10, day11, day12, day13, day14, day15, day16, day2, day3, day4, day5, day6, day7,
+    day8, day9,
 };
 use criterion::{black_box, Criterion};
 use std::env;
@@ -106,6 +107,12 @@ fn aoc2024_bench(c: &mut Criterion) -> io::Result<()> {
     g.bench_function("part 2", |b| b.iter(|| day15::part2(black_box(&data))));
     g.finish();
 
+    let data = get_day_input(16)?;
+    let mut g = c.benchmark_group("day 16");
+    g.bench_function("part 1", |b| b.iter(|| day16::part1(black_box(&data))));
+    g.bench_function("part 2", |b| b.iter(|| day16::part2(black_box(&data))));
+    g.finish();
+
     Ok(())
 }
 

rs/src/day16.rs

@@ -0,0 +1,158 @@
+use if_chain::if_chain;
+use std::cmp::Reverse;
+use std::collections::{BTreeMap, BTreeSet, BinaryHeap};
+
+type YX = (usize, usize);
+
+fn parse(data: &str) -> Option<(BTreeSet<YX>, YX, YX)> {
+    let mut maze = BTreeSet::new();
+    let mut start = None;
+    let mut end = None;
+    for (y, line) in data.lines().enumerate() {
+        for (x, b) in line.bytes().enumerate() {
+            match b {
+                b'#' => {
+                    maze.insert((y, x));
+                }
+                b'S' => {
+                    if start.replace((y, x)).is_some() {
+                        return None;
+                    }
+                }
+                b'E' => {
+                    if end.replace((y, x)).is_some() {
+                        return None;
+                    }
+                }
+                _ => {}
+            }
+        }
+    }
+    Some((maze, start?, end?))
+}
+
+pub fn part1(data: &str) -> Option<usize> {
+    let (maze, start, end) = parse(data)?;
+    let mut queue: BinaryHeap<_> = [(Reverse(0), start, (0, 1))].into();
+    let mut visited = BTreeSet::new();
+    while let Some((Reverse(score), (y, x), (dy, dx))) = queue.pop() {
+        if !visited.insert(((y, x), (dy, dx))) {
+            continue;
+        }
+        if (y, x) == end {
+            return Some(score);
+        }
+        for (score, (dy, dx)) in [
+            (score + 1, (dy, dx)),
+            (score + 1001, (-dx, dy)),
+            (score + 1001, (dx, -dy)),
+        ] {
+            if_chain! {
+                if let Some(y) = y.checked_add_signed(dy);
+                if let Some(x) = x.checked_add_signed(dx);
+                if !maze.contains(&(y, x));
+                then {
+                    queue.push((Reverse(score), (y, x), (dy, dx)));
+                }
+            }
+        }
+    }
+    None
+}
+
+pub fn part2(data: &str) -> Option<usize> {
+    let (maze, start, end) = parse(data)?;
+    let mut best = None;
+    let mut acc = BTreeSet::new();
+    let mut queue: BinaryHeap<(_, _, _, BTreeSet<_>)> =
+        [(Reverse(0), start, (0, 1), [start].into())].into();
+    let mut visited = BTreeMap::new();
+    while let Some((Reverse(score), (y, x), (dy, dx), mut path)) = queue.pop() {
+        if best.filter(|best| *best < score).is_some() {
+            break;
+        }
+        if *visited.entry(((y, x), (dy, dx))).or_insert(score) < score {
+            continue;
+        }
+        if (y, x) == end {
+            best = Some(score);
+            acc.append(&mut path);
+            continue;
+        }
+        for (score, (dy, dx)) in [
+            (score + 1, (dy, dx)),
+            (score + 1001, (-dx, dy)),
+            (score + 1001, (dx, -dy)),
+        ] {
+            if_chain! {
+                if let Some(y) = y.checked_add_signed(dy);
+                if let Some(x) = x.checked_add_signed(dx);
+                if !maze.contains(&(y, x));
+                then {
+                    let mut path = path.clone();
+                    if path.insert((y, x)) {
+                        queue.push((Reverse(score), (y, x), (dy, dx), path));
+                    }
+                }
+            }
+        }
+    }
+    Some(acc.len())
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use indoc::indoc;
+    use pretty_assertions::assert_eq;
+
+    static EXAMPLE_1: &str = indoc! {"
+        ###############
+        #.......#....E#
+        #.#.###.#.###.#
+        #.....#.#...#.#
+        #.###.#####.#.#
+        #.#.#.......#.#
+        #.#.#####.###.#
+        #...........#.#
+        ###.#.#####.#.#
+        #...#.....#.#.#
+        #.#.#.###.#.#.#
+        #.....#...#.#.#
+        #.###.#.#.#.#.#
+        #S..#.....#...#
+        ###############
+    "};
+
+    static EXAMPLE_2: &str = indoc! {"
+        #################
+        #...#...#...#..E#
+        #.#.#.#.#.#.#.#.#
+        #.#.#.#...#...#.#
+        #.#.#.#.###.#.#.#
+        #...#.#.#.....#.#
+        #.#.#.#.#.#####.#
+        #.#...#.#.#.....#
+        #.#.#####.#.###.#
+        #.#.#.......#...#
+        #.#.###.#####.###
+        #.#.#...#.....#.#
+        #.#.#.#####.###.#
+        #.#.#.........#.#
+        #.#.#.#########.#
+        #S#.............#
+        #################
+    "};
+
+    #[test]
+    fn part1_examples() {
+        assert_eq!(Some(7036), part1(EXAMPLE_1));
+        assert_eq!(Some(11048), part1(EXAMPLE_2));
+    }
+
+    #[test]
+    fn part2_examples() {
+        assert_eq!(Some(45), part2(EXAMPLE_1));
+        assert_eq!(Some(64), part2(EXAMPLE_2));
+    }
+}

rs/src/lib.rs

@@ -5,6 +5,7 @@ pub mod day12;
 pub mod day13;
 pub mod day14;
 pub mod day15;
+pub mod day16;
 pub mod day2;
 pub mod day3;
 pub mod day4;

rs/src/main.rs

@@ -1,6 +1,7 @@
 use anyhow::anyhow;
 use aoc2024::{
-    day1, day10, day11, day12, day13, day14, day15, day2, day3, day4, day5, day6, day7, day8, day9,
+    day1, day10, day11, day12, day13, day14, day15, day16, day2, day3, day4, day5, day6, day7,
+    day8, day9,
 };
 use std::collections::HashSet;
 use std::env;
@@ -139,5 +140,13 @@ fn main() -> anyhow::Result<()> {
         println!();
     }
 
+    if args.is_empty() || args.contains("16") {
+        println!("Day 16");
+        let data = get_day_input(16)?;
+        println!("{:?}", day16::part1(&data).ok_or(anyhow!("None"))?);
+        println!("{:?}", day16::part2(&data).ok_or(anyhow!("None"))?);
+        println!();
+    }
+
     Ok(())
 }