solution: day 11

data/examples/11.txt

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

src/bin/11.rs

@@ -0,0 +1,78 @@
+use std::collections::HashSet;
+
+fn parse_input(input: &str) -> (Vec<(usize, usize)>, HashSet<usize>, HashSet<usize>) {
+    let mut galaxies = Vec::new();
+    let mut rows = HashSet::new();
+    let mut columns = HashSet::from_iter(1..(input.lines().next().unwrap().len()));
+
+    for (y, line) in input.lines().enumerate() {
+        let mut found = false;
+        for (x, c) in line.chars().enumerate() {
+            if c == '#' {
+                galaxies.push((y, x));
+                found = true;
+            }
+            columns.remove(&x);
+        }
+        if !found {
+            rows.insert(y);
+        }
+    }
+
+    (galaxies, rows, columns)
+}
+
+fn solve(input: &str, explode: usize) -> Option<usize> {
+    let (galaxies, rows, columns) = parse_input(input);
+
+    let mut counter = 0;
+
+    for ((y1, x1), (y2, x2)) in galaxies
+        .iter()
+        .copied()
+        .enumerate()
+        .flat_map(|(i, x)| galaxies.iter().skip(i + 1).copied().map(move |y| (x, y)))
+    {
+        let y_abs = y1.abs_diff(y2);
+        let x_abs = x1.abs_diff(x2);
+        let x_extra = columns
+            .iter()
+            .filter(|x| (x1..=x2).contains(x) || (x2..=x1).contains(x))
+            .count();
+        let y_extra = rows
+            .iter()
+            .filter(|y| (y1..=y2).contains(y) || (y2..=y1).contains(y))
+            .count();
+        counter += x_abs + y_abs + (x_extra + y_extra) * (explode - 1);
+    }
+
+    Some(counter)
+}
+
+pub fn part_one(input: &str) -> Option<usize> {
+    solve(input, 2)
+}
+
+pub fn part_two(input: &str) -> Option<usize> {
+    solve(input, 1_000_000)
+}
+
+aoc::solution!(11);
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    #[test]
+    fn test_part_one() {
+        assert_eq!(
+            part_one(&aoc::template::read_file("examples", 11)),
+            Some(374)
+        );
+    }
+    #[test]
+    fn test_part_two() {
+        let input = aoc::template::read_file("examples", 11);
+        assert_eq!(solve(&input, 10), Some(1030));
+        assert_eq!(solve(&input, 100), Some(8410));
+    }
+}