Day 11: Cosmic Expansion

ephemient · Dec 11, 2023 · 0f3fcd9 · 0f3fcd9
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diff --git a/README.md b/README.md
@@ -15,4 +15,4 @@ Development occurs in language-specific directories:
 |[Day8.hs](hs/src/Day8.hs)|[Day8.kt](kt/aoc2023-lib/src/commonMain/kotlin/com/github/ephemient/aoc2023/Day8.kt)|[day8.py](py/aoc2023/day8.py)|[day8.rs](rs/src/day8.rs)|
 |[Day9.hs](hs/src/Day9.hs)|[Day9.kt](kt/aoc2023-lib/src/commonMain/kotlin/com/github/ephemient/aoc2023/Day9.kt)|[day9.py](py/aoc2023/day9.py)|[day9.rs](rs/src/day9.rs)|
 |[Day10.hs](hs/src/Day10.hs)|[Day10.kt](kt/aoc2023-lib/src/commonMain/kotlin/com/github/ephemient/aoc2023/Day10.kt)|[day10.py](py/aoc2023/day10.py)|[day10.rs](rs/src/day10.rs)|
-|[Day11.hs](hs/src/Day11.hs)|[Day11.kt](kt/aoc2023-lib/src/commonMain/kotlin/com/github/ephemient/aoc2023/Day11.kt)|[day11.py](py/aoc2023/day11.py)||
+|[Day11.hs](hs/src/Day11.hs)|[Day11.kt](kt/aoc2023-lib/src/commonMain/kotlin/com/github/ephemient/aoc2023/Day11.kt)|[day11.py](py/aoc2023/day11.py)|[day11.rs](rs/src/day11.rs)|
diff --git a/rs/benches/criterion.rs b/rs/benches/criterion.rs
@@ -1,4 +1,4 @@
-use aoc2023::{day1, day10, day2, day3, day4, day5, day6, day7, day8, day9};
+use aoc2023::{day1, day10, day11, day2, day3, day4, day5, day6, day7, day8, day9};
 use criterion::{black_box, Criterion};
 use std::env;
 use std::fs;
@@ -74,6 +74,12 @@ fn aoc2023_bench(c: &mut Criterion) -> io::Result<()> {
     g.bench_function("part 2", |b| b.iter(|| day10::part2(black_box(&data))));
     g.finish();
 
+    let data = get_day_input(11)?;
+    let mut g = c.benchmark_group("day 11");
+    g.bench_function("part 1", |b| b.iter(|| day11::part1(black_box(&data))));
+    g.bench_function("part 2", |b| b.iter(|| day11::part2(black_box(&data))));
+    g.finish();
+
     Ok(())
 }
 

diff --git a/rs/src/day11.rs b/rs/src/day11.rs
@@ -0,0 +1,85 @@
+fn solve(data: &str, n: u64) -> u64 {
+    let lines = data.lines().collect::<Vec<_>>();
+    let rows = lines
+        .iter()
+        .enumerate()
+        .filter_map(|(y, line)| {
+            if line.chars().any(|c| c == '#') {
+                None
+            } else {
+                Some(y)
+            }
+        })
+        .collect::<Vec<_>>();
+    let cols = (0..lines
+        .iter()
+        .map(|line| line.len())
+        .max()
+        .unwrap_or_default())
+        .filter(|&x| lines.iter().all(|line| !line[x..].starts_with('#')))
+        .collect::<Vec<_>>();
+    let galaxies = lines
+        .iter()
+        .enumerate()
+        .flat_map(|(y, line)| {
+            line.char_indices()
+                .filter_map(move |(x, c)| if c == '#' { Some((y, x)) } else { None })
+        })
+        .collect::<Vec<_>>();
+    galaxies
+        .iter()
+        .enumerate()
+        .flat_map(|(i, (y0, x0))| {
+            let rows = &rows;
+            let cols = &cols;
+            galaxies[i + 1..].iter().map(move |(y1, x1)| {
+                let (x0, x1) = (x0.min(x1), x0.max(x1));
+                (y1 - y0 + x1 - x0) as u64
+                    + (n - 1)
+                        * (rows.binary_search(y1).unwrap_err()
+                            - rows.binary_search(y0).unwrap_err()
+                            + cols.binary_search(x1).unwrap_err()
+                            - cols.binary_search(x0).unwrap_err()) as u64
+            })
+        })
+        .sum()
+}
+
+pub fn part1(data: &str) -> u64 {
+    solve(data, 2)
+}
+
+pub fn part2(data: &str) -> u64 {
+    solve(data, 1000000)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use indoc::indoc;
+    use pretty_assertions::assert_eq;
+
+    static EXAMPLE: &str = indoc! {"
+        ...#......
+        .......#..
+        #.........
+        ..........
+        ......#...
+        .#........
+        .........#
+        ..........
+        .......#..
+        #...#.....
+    "};
+
+    #[test]
+    fn part1_examples() {
+        assert_eq!(374, solve(EXAMPLE, 2));
+    }
+
+    #[test]
+    fn part2_examples() {
+        assert_eq!(1030, solve(EXAMPLE, 10));
+        assert_eq!(8410, solve(EXAMPLE, 100));
+    }
+}
diff --git a/rs/src/lib.rs b/rs/src/lib.rs
@@ -1,5 +1,6 @@
 pub mod day1;
 pub mod day10;
+pub mod day11;
 pub mod day2;
 pub mod day3;
 pub mod day4;

diff --git a/rs/src/main.rs b/rs/src/main.rs
@@ -1,4 +1,4 @@
-use aoc2023::{day1, day10, day2, day3, day4, day5, day6, day7, day8, day9};
+use aoc2023::{day1, day10, day11, day2, day3, day4, day5, day6, day7, day8, day9};
 use std::collections::HashSet;
 use std::env;
 use std::fs;
@@ -96,5 +96,13 @@ fn main() -> io::Result<()> {
         println!();
     }
 
+    if args.is_empty() || args.contains("11") {
+        println!("Day 11");
+        let data = get_day_input(11)?;
+        println!("{:?}", day11::part1(&data));
+        println!("{:?}", day11::part2(&data));
+        println!();
+    }
+
     Ok(())
 }