day 8 part 1

src/day08.rs

@@ -0,0 +1,72 @@
+use std::{collections::HashSet, fs::read_to_string};
+
+use itertools::Itertools;
+
+use crate::utils::grid::Grid;
+
+pub fn day_main() {
+    let input = read_to_string("input/day08.txt").unwrap();
+    let input = input.trim();
+    println!(" part1: {}", part1(input));
+    println!(" part2: {}", part2(input));
+}
+
+type RiddleResult = usize;
+
+fn part1(input: &str) -> RiddleResult {
+    let grid = Grid::parse(input);
+    let mut antinodes = HashSet::new();
+    let antennas = grid
+        .entries()
+        .filter(|(_, c)| **c != '.')
+        .into_group_map_by(|(_, c)| *c);
+    for (frequency, coords) in antennas {
+        for (a, _) in coords.iter() {
+            for (b, _) in coords.iter() {
+                if a == b {
+                    continue;
+                }
+                let dx = a.0 - b.0;
+                let dy = a.1 - b.1;
+                let p = (a.0 + dx, a.1 + dy);
+                if grid.contains_key(p) {
+                    antinodes.insert(p);
+                }
+            }
+        }
+    }
+    antinodes.len()
+}
+
+fn part2(_input: &str) -> RiddleResult {
+    0
+}
+
+#[cfg(test)]
+mod test {
+    use super::{part1, part2};
+
+    const TEST_INPUT: &str = r"............
+........0...
+.....0......
+.......0....
+....0.......
+......A.....
+............
+............
+........A...
+.........A..
+............
+............
+";
+
+    #[test]
+    fn test1() {
+        assert_eq!(part1(TEST_INPUT), 14);
+    }
+
+    #[test]
+    fn test2() {
+        assert_eq!(part2(TEST_INPUT), 0);
+    }
+}

src/lib.rs

@@ -5,4 +5,5 @@ pub mod day04;
 pub mod day05;
 pub mod day06;
 pub mod day07;
+pub mod day08;
 pub mod utils;

src/main.rs

@@ -12,6 +12,7 @@ fn main() {
         (5, day05::day_main),
         (6, day06::day_main),
         (7, day07::day_main),
+        (8, day08::day_main),
     ]);
     let day: Option<u8> = args().nth(1).and_then(|a| a.parse().ok());
     let Some(day) = day else {