Solve day 11

input/11-test

@@ -0,0 +1,10 @@
+...#......
+.......#..
+#.........
+..........
+......#...
+.#........
+.........#
+..........
+.......#..
+#...#.....

src/bin/11.rs

@@ -0,0 +1,96 @@
+use aoc2023::*;
+use itertools::Itertools;
+
+const INPUT: &str = include_str!("../../input/11");
+
+fn main() {
+    assert_example!(part1, "11-test", 374);
+    println!("Part 1: {}", part1(INPUT));
+    assert_example!(part2, "11-test", 82000210);
+    println!("Part 2: {}", part2(INPUT));
+}
+
+fn part1(input: &str) -> usize {
+    let mut universe = Universe::parse(input);
+    universe.expand(2);
+    universe.sum_of_distances()
+}
+
+fn part2(input: &str) -> usize {
+    let mut universe = Universe::parse(input);
+    universe.expand(1_000_000);
+    universe.sum_of_distances()
+}
+
+type Galaxy = Vec2<usize>;
+
+struct Universe {
+    galaxies: Vec<Galaxy>,
+}
+
+impl Universe {
+    fn expand(&mut self, factor: usize) {
+        let add = factor - 1;
+        let dimensions = self.dimensions();
+
+        // Add additional columns
+        for x in (0..=dimensions.x).rev() {
+            let any_galaxies = self.galaxies.iter().any(|g| g.x == x);
+            if any_galaxies {
+                continue;
+            }
+
+            self.galaxies
+                .iter_mut()
+                .filter(|g| g.x > x)
+                .for_each(|g| g.x += add);
+        }
+
+        // Add additional rows
+        for y in (0..=dimensions.y).rev() {
+            let any_galaxies = self.galaxies.iter().any(|g| g.y == y);
+            if any_galaxies {
+                continue;
+            }
+
+            self.galaxies
+                .iter_mut()
+                .filter(|g| g.y > y)
+                .for_each(|g| g.y += add);
+        }
+    }
+
+    fn dimensions(&self) -> Galaxy {
+        self.galaxies.iter().fold(Galaxy::default(), |a, b| Galaxy {
+            x: a.x.max(b.x),
+            y: a.y.max(b.y),
+        })
+    }
+
+    fn sum_of_distances(&self) -> usize {
+        let pairs = self
+            .galaxies
+            .iter()
+            .copied()
+            .combinations_with_replacement(2)
+            .map(|list| (list[0], list[1]));
+        pairs.map(distance).sum()
+    }
+
+    fn parse(input: &str) -> Self {
+        let galaxies = input.lines().enumerate().flat_map(parse_line).collect();
+        Self { galaxies }
+    }
+}
+
+fn parse_line((line_index, line): (usize, &str)) -> impl Iterator<Item = Galaxy> + '_ {
+    line.chars()
+        .enumerate()
+        .filter(|&(_x, c)| c == '#')
+        .map(move |(x, _c)| Vec2::new(x, line_index))
+}
+
+/// Taxi cab distance between two galaxies.
+fn distance((a, b): (Galaxy, Galaxy)) -> usize {
+    a.x.abs_diff(b.x) + a.y.abs_diff(b.y)
+}