Day 23: Unstable Diffusion

ephemient · Dec 23, 2022 · 4c0e48d · 4c0e48d
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diff --git a/README.md b/README.md
@@ -28,4 +28,4 @@ Development occurs in language-specific directories:
 |[Day20.hs](hs/src/Day20.hs)|[Day20.kt](kt/src/commonMain/kotlin/com/github/ephemient/aoc2022/Day20.kt)|[day20.py](py/aoc2022/day20.py)|[day20.rs](rs/src/day20.rs)|
 |[Day21.hs](hs/src/Day21.hs)|[Day21.kt](kt/src/commonMain/kotlin/com/github/ephemient/aoc2022/Day21.kt)|[day21.py](py/aoc2022/day21.py)|[day21.rs](rs/src/day21.rs)|
 |[Day22.hs](hs/src/Day22.hs)|[Day22.kt](kt/src/commonMain/kotlin/com/github/ephemient/aoc2022/Day22.kt)|[day22.py](py/aoc2022/day22.py)|[day22.rs](rs/src/day22.rs)|
-|[Day23.hs](hs/src/Day23.hs)|[Day23.kt](kt/src/commonMain/kotlin/com/github/ephemient/aoc2022/Day23.kt)|[day23.py](py/aoc2022/day23.py)|
+|[Day23.hs](hs/src/Day23.hs)|[Day23.kt](kt/src/commonMain/kotlin/com/github/ephemient/aoc2022/Day23.kt)|[day23.py](py/aoc2022/day23.py)|[day23.rs](rs/src/day23.rs)|
diff --git a/rs/benches/criterion.rs b/rs/benches/criterion.rs
@@ -3,7 +3,7 @@ extern crate build_const;
 
 use aoc2022::{
     day1, day10, day11, day12, day13, day13_fast, day14, day15, day16, day17, day18, day19, day2,
-    day20, day21, day22, day3, day4, day5, day6, day7, day8, day9,
+    day20, day21, day22, day23, day3, day4, day5, day6, day7, day8, day9,
 };
 use criterion::{black_box, criterion_group, criterion_main, Criterion};
 use gag::Gag;
@@ -111,6 +111,10 @@ fn aoc2022_bench(c: &mut Criterion) {
     g.bench_function("part 1", |b| b.iter(|| day22::part1(black_box(DAY22))));
     g.bench_function("part 2", |b| b.iter(|| day22::part2(black_box(DAY22))));
     g.finish();
+    let mut g = c.benchmark_group("day 23");
+    g.bench_function("part 1", |b| b.iter(|| day23::part1(black_box(DAY23))));
+    g.bench_function("part 2", |b| b.iter(|| day23::part2(black_box(DAY23))));
+    g.finish();
 }
 
 criterion_group!(aoc2022, aoc2022_bench);

diff --git a/rs/src/day23.rs b/rs/src/day23.rs
@@ -0,0 +1,150 @@
+use self::Direction::*;
+use std::array;
+use std::cmp::{max, min};
+use std::collections::{BTreeMap, BTreeSet};
+use std::iter::Cycle;
+
+#[derive(Clone, Copy)]
+enum Direction {
+    N,
+    S,
+    W,
+    E,
+}
+
+fn directions() -> Cycle<array::IntoIter<[Direction; 4], 4>> {
+    [[N, S, W, E], [S, W, E, N], [W, E, N, S], [E, N, S, W]]
+        .into_iter()
+        .cycle()
+}
+
+fn sides(direction: Direction, x: isize, y: isize) -> [(isize, isize); 3] {
+    match direction {
+        N => [x - 1, x, x + 1].map(|x| (x, y - 1)),
+        S => [x - 1, x, x + 1].map(|x| (x, y + 1)),
+        W => [y - 1, y, y + 1].map(|y| (x - 1, y)),
+        E => [y - 1, y, y + 1].map(|y| (x + 1, y)),
+    }
+}
+
+fn r#move(direction: Direction, x: isize, y: isize) -> (isize, isize) {
+    match direction {
+        N => (x, y - 1),
+        S => (x, y + 1),
+        W => (x - 1, y),
+        E => (x + 1, y),
+    }
+}
+
+fn neighbors(x: isize, y: isize) -> [(isize, isize); 8] {
+    [
+        (x - 1, y - 1),
+        (x - 1, y),
+        (x - 1, y + 1),
+        (x, y - 1),
+        (x, y + 1),
+        (x + 1, y - 1),
+        (x + 1, y),
+        (x + 1, y + 1),
+    ]
+}
+
+fn parse<'a, I, S>(lines: I) -> BTreeSet<(isize, isize)>
+where
+    I: IntoIterator<Item = &'a S>,
+    S: AsRef<str> + 'a,
+{
+    lines
+        .into_iter()
+        .enumerate()
+        .flat_map(|(y, line)| {
+            line.as_ref()
+                .chars()
+                .enumerate()
+                .filter(|(_, c)| c == &'#')
+                .map(move |(x, _)| (x as isize, y as isize))
+        })
+        .collect()
+}
+
+fn step(state: &BTreeSet<(isize, isize)>, directions: &[Direction]) -> BTreeSet<(isize, isize)> {
+    let mut proposals = BTreeMap::new();
+    for &(x, y) in state {
+        if !neighbors(x, y).iter().any(|point| state.contains(point)) {
+            continue;
+        }
+        if let Some(&direction) = directions.iter().find(|&&direction| {
+            !sides(direction, x, y)
+                .iter()
+                .any(|point| state.contains(point))
+        }) {
+            proposals
+                .entry(r#move(direction, x, y))
+                .and_modify(|e: &mut Vec<_>| e.push((x, y)))
+                .or_insert_with(|| vec![(x, y)]);
+        }
+    }
+    proposals.retain(|_, old| old.len() == 1);
+    let mut state = state.clone();
+    for (new, old) in proposals {
+        state.remove(&old[0]);
+        state.insert(new);
+    }
+    state
+}
+
+pub fn part1<'a, I, S>(lines: I) -> usize
+where
+    I: IntoIterator<Item = &'a S>,
+    S: AsRef<str> + 'a,
+{
+    let state = directions()
+        .take(10)
+        .fold(parse(lines), |state, directions| step(&state, &directions));
+    let (min_x, max_x, min_y, max_y) = state.iter().fold(
+        (isize::MAX, isize::MIN, isize::MAX, isize::MIN),
+        |(min_x, max_x, min_y, max_y), &(x, y)| {
+            (min(min_x, x), max(max_x, x), min(min_y, y), max(max_y, y))
+        },
+    );
+    (max_x - min_x + 1) as usize * (max_y - min_y + 1) as usize - state.len()
+}
+
+pub fn part2<'a, I, S>(lines: I) -> usize
+where
+    I: IntoIterator<Item = &'a S>,
+    S: AsRef<str> + 'a,
+{
+    directions()
+        .scan(parse(lines), |state, directions| {
+            let next = step(state, &directions);
+            if state != &next {
+                *state = next;
+                Some(())
+            } else {
+                None
+            }
+        })
+        .count()
+        + 1
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use pretty_assertions::assert_eq;
+
+    static EXAMPLE: &[&str] = &[
+        "....#..", "..###.#", "#...#.#", ".#...##", "#.###..", "##.#.##", ".#..#..",
+    ];
+
+    #[test]
+    fn part1_examples() {
+        assert_eq!(110, part1(EXAMPLE));
+    }
+
+    #[test]
+    fn part2_examples() {
+        assert_eq!(20, part2(EXAMPLE));
+    }
+}
diff --git a/rs/src/lib.rs b/rs/src/lib.rs
@@ -14,6 +14,7 @@ pub mod day2;
 pub mod day20;
 pub mod day21;
 pub mod day22;
+pub mod day23;
 pub mod day3;
 pub mod day4;
 pub mod day5;

diff --git a/rs/src/main.rs b/rs/src/main.rs
@@ -3,7 +3,7 @@ extern crate build_const;
 
 use aoc2022::{
     day1, day10, day11, day12, day13, day13_fast, day14, day15, day16, day17, day18, day19, day2,
-    day20, day21, day22, day3, day4, day5, day6, day7, day8, day9,
+    day20, day21, day22, day23, day3, day4, day5, day6, day7, day8, day9,
 };
 use std::collections::HashSet;
 use std::env;
@@ -177,5 +177,12 @@ fn main() -> io::Result<()> {
         println!();
     }
 
+    if args.is_empty() || args.contains("23") {
+        println!("Day 23");
+        println!("{:?}", day23::part1(DAY23));
+        println!("{:?}", day23::part2(DAY23));
+        println!();
+    }
+
     Ok(())
 }