[2024] Day 8 initial solution

Author: connorslade

README.md

@@ -12,6 +12,7 @@ Thank you to [Eric Wastl](http://was.tl) for running this incredible yearly even
 - [Day 05: Print Queue](aoc_2024/src/day_05.rs)
 - [Day 06: Guard Gallivant](aoc_2024/src/day_06.rs)
 - [Day 07: Bridge Repair](aoc_2024/src/day_07.rs)
+- [Day 08: Resonant Collinearity](aoc_2024/src/day_08.rs)
 <!-- MARKER -->
 
 ## [2023](https://adventofcode.com/2023) [![aoc_2023](https://github.com/connorslade/advent-of-code/actions/workflows/aoc_2023.yml/badge.svg)](https://github.com/connorslade/advent-of-code/actions/workflows/aoc_2023.yml)

aoc_2024/src/day_08.rs

@@ -0,0 +1,150 @@
+use std::collections::{HashMap, HashSet};
+
+use aoc_lib::matrix::Matrix;
+use common::{solution, Answer};
+use nd_vec::{vector, Vec2};
+
+use itertools::Itertools;
+
+solution!("Resonant Collinearity", 8);
+
+#[derive(Clone)]
+enum Tile {
+    Emitter(char),
+    Empty,
+}
+
+fn part_a(input: &str) -> Answer {
+    let world = Matrix::new_chars(input, |x| match x {
+        'a'..='z' | 'A'..='Z' | '0'..='9' => Tile::Emitter(x),
+        _ => Tile::Empty,
+    });
+
+    let mut freqs = HashMap::<char, Vec<Vec2<i32>>>::new();
+
+    // oh god just make a Matrix.iter function at this point...
+    for x in 0..world.size.x() {
+        for y in 0..world.size.y() {
+            let pos = vector!(x, y);
+            if let Tile::Emitter(chr) = world.get(pos).unwrap() {
+                freqs
+                    .entry(*chr)
+                    .or_default()
+                    .push(pos.try_cast::<i32>().unwrap());
+            }
+        }
+    }
+
+    // nodes are on the line between two of the same freq emitters when d1 = 2*d2
+    // to find nodes, start by finding all lines through matching emitters
+
+    let in_bounds = |pos: Vec2<i32>| {
+        pos.x() >= 0
+            && pos.y() >= 0
+            && pos.x() < world.size.x() as i32
+            && pos.y() < world.size.y() as i32
+    };
+
+    let mut out = HashSet::new();
+    for (_freq, pos) in freqs {
+        for (a, b) in pos.into_iter().tuple_combinations() {
+            let diff_a = a + (a - b);
+            let diff_b = b + (b - a);
+
+            if in_bounds(diff_a) {
+                out.insert(diff_a);
+            }
+
+            if in_bounds(diff_b) {
+                out.insert(diff_b);
+            }
+        }
+    }
+
+    out.len().into()
+}
+
+fn part_b(input: &str) -> Answer {
+    let world = Matrix::new_chars(input, |x| match x {
+        'a'..='z' | 'A'..='Z' | '0'..='9' => Tile::Emitter(x),
+        _ => Tile::Empty,
+    });
+
+    let mut freqs = HashMap::<char, Vec<Vec2<i32>>>::new();
+
+    // oh god just make a Matrix.iter function at this point...
+    for x in 0..world.size.x() {
+        for y in 0..world.size.y() {
+            let pos = vector!(x, y);
+            if let Tile::Emitter(chr) = world.get(pos).unwrap() {
+                freqs
+                    .entry(*chr)
+                    .or_default()
+                    .push(pos.try_cast::<i32>().unwrap());
+            }
+        }
+    }
+
+    // nodes are on the line between two of the same freq emitters when d1 = 2*d2
+    // to find nodes, start by finding all lines through matching emitters
+
+    let in_bounds = |pos: Vec2<i32>| {
+        pos.x() >= 0
+            && pos.y() >= 0
+            && pos.x() < world.size.x() as i32
+            && pos.y() < world.size.y() as i32
+    };
+
+    let mut out = HashSet::new();
+    for (_freq, pos) in freqs {
+        for (a, b) in pos.into_iter().tuple_combinations() {
+            let diff_a = a - b;
+            let diff_b = b - a;
+
+            let mut pos_a = a;
+            let mut pos_b = b;
+
+            while in_bounds(pos_a) {
+                out.insert(pos_a);
+                pos_a += diff_a;
+            }
+
+            while in_bounds(pos_b) {
+                out.insert(pos_b);
+                pos_b += diff_b;
+            }
+        }
+    }
+
+    out.len().into()
+}
+
+#[cfg(test)]
+mod test {
+    use indoc::indoc;
+
+    const CASE: &str = indoc! {"
+        ............
+        ........0...
+        .....0......
+        .......0....
+        ....0.......
+        ......A.....
+        ............
+        ............
+        ........A...
+        .........A..
+        ............
+        ............
+    "};
+
+    #[test]
+    fn part_a() {
+        assert_eq!(super::part_a(CASE), 14.into());
+    }
+
+    #[test]
+    fn part_b() {
+        assert_eq!(super::part_b(CASE), 34.into());
+    }
+}

aoc_2024/src/lib.rs

@@ -7,6 +7,7 @@ mod day_04;
 mod day_05;
 mod day_06;
 mod day_07;
+mod day_08;
 // [import_marker]
 
 pub const SOLUTIONS: &[Solution] = &[
@@ -17,5 +18,6 @@ pub const SOLUTIONS: &[Solution] = &[
     day_05::SOLUTION,
     day_06::SOLUTION,
     day_07::SOLUTION,
+    day_08::SOLUTION,
     // [list_marker]
 ];