solve: day8

Author: tom-anders

Cargo.toml

@@ -2,7 +2,7 @@
 resolver = "2"
 members = [
     "utils",
-    "aoc_derive", "day1", "day2", "day3", "day4", "day5", "day6", "day7",
+    "aoc_derive", "day1", "day2", "day3", "day4", "day5", "day6", "day7", "day8",
 ]
 
 [workspace.dependencies]

day8/Cargo.toml

@@ -0,0 +1,18 @@
+[package]
+name = "day8"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
+aoc_derive.path = '../aoc_derive'
+utils.path = '../utils'
+derive_more.workspace = true
+itertools.workspace = true
+lazy-regex.workspace = true
+parse-display.workspace = true
+rayon.workspace = true
+regex.workspace = true
+num.workspace = true
+
+[dev-dependencies]
+pretty_assertions.workspace = true

day8/src/main.rs

@@ -0,0 +1,83 @@
+use std::{collections::HashMap, ops::ControlFlow};
+
+use aoc_derive::aoc_main;
+use grid::Grid;
+use itertools::Itertools;
+use math::Vec2D;
+use utils::*;
+
+fn antinodes_part2(a: Vec2D, b: Vec2D, grid: &Grid<char>) -> impl Iterator<Item = Vec2D> {
+    let mut antinodes = vec![];
+    let mut pos = a;
+    while grid.contains(&pos) {
+        antinodes.push(pos);
+        pos += a - b;
+    }
+    antinodes.into_iter()
+}
+
+#[aoc_main]
+fn solve(input: Input) -> impl Into<Solution> {
+    let grid = input.char_grid();
+
+    let antenna_map = grid.iter().filter_map(|(pos, &c)| (c != '.').then_some((c, pos))).fold(
+        HashMap::<_, Vec<_>>::new(),
+        |mut map, (c, pos)| {
+            map.entry(c).or_default().push(pos);
+            map
+        },
+    );
+
+    let part1 = antenna_map
+        .iter()
+        .flat_map(|(_, antennas)| {
+            antennas
+                .clone()
+                .into_iter()
+                .combinations(2)
+                .flat_map(|pair| [pair[0] + (pair[0] - pair[1]), pair[1] + (pair[1] - pair[0])])
+                .filter(|antinode| grid.contains(antinode))
+        })
+        .unique()
+        .count();
+
+    let part2 = antenna_map
+        .into_iter()
+        .flat_map(|(_, antennas)| {
+            antennas.clone().into_iter().combinations(2).flat_map(|pair| {
+                antinodes_part2(pair[0], pair[1], &grid)
+                    .chain(antinodes_part2(pair[1], pair[0], &grid))
+            })
+        })
+        .unique()
+        .count();
+
+    (part1, part2)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    #[test]
+    fn test_examples() {
+        use utils::assert_example;
+        assert_example!(
+            r#"............
+........0...
+.....0......
+.......0....
+....0.......
+......A.....
+............
+............
+........A...
+.........A..
+............
+............
+
+                "#,
+            14,
+            34
+        );
+    }
+}