From f34e61c4b007c90e8c4934109f86078e3aef50ed Mon Sep 17 00:00:00 2001
From: Daniel Lin <ephemient@gmail.com>
Date: Sun, 8 Dec 2024 02:17:57 -0500
Subject: [PATCH] Day 8: Resonant Collinearity

---
 README.md               |  2 +-
 rs/benches/criterion.rs |  8 +++-
 rs/src/day8.rs          | 90 +++++++++++++++++++++++++++++++++++++++++
 rs/src/lib.rs           |  1 +
 rs/src/main.rs          | 10 ++++-
 5 files changed, 108 insertions(+), 3 deletions(-)
 create mode 100644 rs/src/day8.rs

diff --git a/README.md b/README.md
index 81a0fcee..c75a6883 100644
--- a/README.md
+++ b/README.md
@@ -12,4 +12,4 @@ Development occurs in language-specific directories:
 |[Day5.hs](hs/src/Day5.hs)|[Day5.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day5.kt)|[day5.py](py/aoc2024/day5.py)|[day5.rs](rs/src/day5.rs)|
 |[Day6.hs](hs/src/Day6.hs)|[Day6.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day6.kt)|[day6.py](py/aoc2024/day6.py)|[day6.rs](rs/src/day6.rs)|
 |[Day7.hs](hs/src/Day7.hs)|[Day7.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day7.kt)|[day7.py](py/aoc2024/day7.py)|[day7.rs](rs/src/day7.rs)|
-|[Day8.hs](hs/src/Day8.hs)|[Day8.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day8.kt)|[day8.py](py/aoc2024/day8.py)||
+|[Day8.hs](hs/src/Day8.hs)|[Day8.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day8.kt)|[day8.py](py/aoc2024/day8.py)|[day8.rs](rs/src/day8.rs)|
diff --git a/rs/benches/criterion.rs b/rs/benches/criterion.rs
index d946b4d9..b454fb08 100644
--- a/rs/benches/criterion.rs
+++ b/rs/benches/criterion.rs
@@ -1,4 +1,4 @@
-use aoc2024::{day1, day2, day3, day4, day5, day6, day7};
+use aoc2024::{day1, day2, day3, day4, day5, day6, day7, day8};
 use criterion::{black_box, Criterion};
 use std::env;
 use std::fs;
@@ -56,6 +56,12 @@ fn aoc2024_bench(c: &mut Criterion) -> io::Result<()> {
     g.bench_function("part 2", |b| b.iter(|| day7::part2(black_box(&data))));
     g.finish();
 
+    let data = get_day_input(8)?;
+    let mut g = c.benchmark_group("day 8");
+    g.bench_function("part 1", |b| b.iter(|| day8::part1(black_box(&data))));
+    g.bench_function("part 2", |b| b.iter(|| day8::part2(black_box(&data))));
+    g.finish();
+
     Ok(())
 }
 
diff --git a/rs/src/day8.rs b/rs/src/day8.rs
new file mode 100644
index 00000000..ddd42135
--- /dev/null
+++ b/rs/src/day8.rs
@@ -0,0 +1,90 @@
+use std::collections::BTreeSet;
+use std::iter;
+
+use itertools::Itertools;
+
+fn solve<I>(data: &str, multiples: I) -> usize
+where
+    I: Clone + Iterator<Item = isize>,
+{
+    let (mut height, mut width) = (0, 0);
+    data.lines()
+        .enumerate()
+        .flat_map(|(y, line)| {
+            height = y + 1;
+            width = width.max(line.len());
+            line.bytes().enumerate().filter_map(move |(x, b)| match b {
+                b'.' => None,
+                _ => Some((b, (y, x))),
+            })
+        })
+        .into_grouping_map_by(|(b, _)| *b)
+        .fold_with(
+            |_, _| vec![],
+            |mut acc, _, (_, point)| {
+                acc.push(point);
+                acc
+            },
+        )
+        .values()
+        .flat_map(|points| {
+            points.iter().flat_map(|point0 @ (y0, x0)| {
+                points
+                    .iter()
+                    .filter(move |point1| point0 != *point1)
+                    .flat_map(|(y1, x1)| {
+                        let (dy, dx) = (*y1 as isize - *y0 as isize, *x1 as isize - *x0 as isize);
+                        multiples
+                            .clone()
+                            .map(move |i| {
+                                y1.checked_add_signed(i * dy)
+                                    .filter(|y| *y < height)
+                                    .zip(x1.checked_add_signed(i * dx).filter(|x| *x < width))
+                            })
+                            .while_some()
+                    })
+            })
+        })
+        .collect::<BTreeSet<_>>()
+        .len()
+}
+
+pub fn part1(data: &str) -> usize {
+    solve(data, iter::once(1))
+}
+
+pub fn part2(data: &str) -> usize {
+    solve(data, iter::successors(Some(0), |i| Some(i + 1)))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use indoc::indoc;
+    use pretty_assertions::assert_eq;
+
+    static EXAMPLE: &str = indoc! {"
+        ............
+        ........0...
+        .....0......
+        .......0....
+        ....0.......
+        ......A.....
+        ............
+        ............
+        ........A...
+        .........A..
+        ............
+        ............
+    "};
+
+    #[test]
+    fn part1_examples() {
+        assert_eq!(14, part1(EXAMPLE));
+    }
+
+    #[test]
+    fn part2_examples() {
+        assert_eq!(34, part2(EXAMPLE));
+    }
+}
diff --git a/rs/src/lib.rs b/rs/src/lib.rs
index da2f9142..65fdb47f 100644
--- a/rs/src/lib.rs
+++ b/rs/src/lib.rs
@@ -5,3 +5,4 @@ pub mod day4;
 pub mod day5;
 pub mod day6;
 pub mod day7;
+pub mod day8;
diff --git a/rs/src/main.rs b/rs/src/main.rs
index 0c506941..5aa1c058 100644
--- a/rs/src/main.rs
+++ b/rs/src/main.rs
@@ -1,5 +1,5 @@
 use anyhow::anyhow;
-use aoc2024::{day1, day2, day3, day4, day5, day6, day7};
+use aoc2024::{day1, day2, day3, day4, day5, day6, day7, day8};
 use std::collections::HashSet;
 use std::env;
 use std::fs;
@@ -73,5 +73,13 @@ fn main() -> anyhow::Result<()> {
         println!();
     }
 
+    if args.is_empty() || args.contains("8") {
+        println!("Day 8");
+        let data = get_day_input(8)?;
+        println!("{:?}", day8::part1(&data));
+        println!("{:?}", day8::part2(&data));
+        println!();
+    }
+
     Ok(())
 }