solution: day 8

data/examples/08.txt

@@ -0,0 +1,12 @@
+............
+........0...
+.....0......
+.......0....
+....0.......
+......A.....
+............
+............
+........A...
+.........A..
+............
+............

src/bin/08.rs

@@ -0,0 +1,104 @@
+use hashbrown::{HashMap, HashSet};
+use itertools::Itertools;
+
+#[allow(clippy::type_complexity)]
+fn parse_input(input: &str) -> (Vec<Vec<char>>, HashMap<char, Vec<(isize, isize)>>) {
+    let grid = input.lines().map(|s| s.chars().collect_vec()).collect_vec();
+
+    let mut antennas: HashMap<char, Vec<(isize, isize)>> = HashMap::new();
+    for (i, row) in grid.iter().enumerate() {
+        for (j, cell) in row.iter().copied().enumerate().filter(|(_, c)| *c != '.') {
+            antennas
+                .entry(cell)
+                .or_default()
+                .push((i as isize, j as isize));
+        }
+    }
+
+    (grid, antennas)
+}
+
+pub fn part_one(input: &str) -> Option<usize> {
+    let (grid, antennas) = parse_input(input);
+
+    let mut set = HashSet::new();
+    for v in antennas.values() {
+        for (s, (i, j)) in v.iter().copied().enumerate() {
+            for (ii, jj) in v.iter().copied().skip(s + 1) {
+                let (di, dj) = (i - ii, j - jj);
+
+                let (a00, a01) = (i + di, j + dj);
+                let (a10, a11) = (ii - di, jj - dj);
+
+                if grid
+                    .get(a00 as usize)
+                    .and_then(|row| row.get(a01 as usize))
+                    .is_some()
+                {
+                    set.insert((a00, a01));
+                }
+
+                if grid
+                    .get(a10 as usize)
+                    .and_then(|row| row.get(a11 as usize))
+                    .is_some()
+                {
+                    set.insert((a10, a11));
+                }
+            }
+        }
+    }
+
+    set.len().into()
+}
+
+pub fn part_two(input: &str) -> Option<usize> {
+    let (grid, antennas) = parse_input(input);
+
+    let mut set = HashSet::new();
+    for v in antennas.values() {
+        for (s, (i, j)) in v.iter().copied().enumerate() {
+            for (ii, jj) in v.iter().copied().skip(s + 1) {
+                let (di, dj) = (i - ii, j - jj);
+
+                let (mut a00, mut a01) = (i, j);
+                let (mut a10, mut a11) = (ii, jj);
+
+                while grid
+                    .get(a00 as usize)
+                    .and_then(|r| r.get(a01 as usize))
+                    .is_some()
+                {
+                    set.insert((a00, a01));
+                    (a00, a01) = (a00 + di, a01 + dj);
+                }
+
+                while grid
+                    .get(a10 as usize)
+                    .and_then(|r| r.get(a11 as usize))
+                    .is_some()
+                {
+                    set.insert((a10, a11));
+                    (a10, a11) = (a10 - di, a11 - dj);
+                }
+            }
+        }
+    }
+
+    set.len().into()
+}
+
+aoc::solution!(8);
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    #[test]
+    fn test_part_one() {
+        assert_eq!(part_one(&aoc::template::read_file("examples", 8)), Some(14));
+    }
+    #[test]
+    fn test_part_two() {
+        assert_eq!(part_two(&aoc::template::read_file("examples", 8)), Some(34));
+    }
+}