From cfe1a0f1c93e8e6e3bb88fcb2be6ea9c7023dfc2 Mon Sep 17 00:00:00 2001
From: Jordan Doyle <jordan@doyle.la>
Date: Sun, 08 Dec 2024 15:14:34 +0000
Subject: [PATCH] Add 2024 day 8

---
 Cargo.toml |  4 ++++
 README     |  4 ++--
 2024/08.rs | 65 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 71 insertions(+), 2 deletions(-)

diff --git a/Cargo.toml b/Cargo.toml
index fc0c471..254d04e 100644
--- a/Cargo.toml
+++ a/Cargo.toml
@@ -38,6 +38,10 @@
 name = "aoc2024-07"
 path = "2024/07.rs"
 
+[[bin]]
+name = "aoc2024-08"
+path = "2024/08.rs"
+
 [profile.release]
 overflow-checks = true
 
diff --git a/README b/README
index 6244692..02fb2af 100644
--- a/README
+++ a/README
@@ -21,8 +21,8 @@
 |        5 | PHP      | |        5 | Rust     | |        5 | HCL/TF   |
 |        6 | Zig      | |        6 | Haskell  | |        6 | Apache2  |
 |        7 | Rust     | |        7 | Haskell  | +---------------------+
-+---------------------+ |        8 | Haskell  |
-                        |        9 | Haskell  |
+|        8 | Rust     | |        8 | Haskell  |
++---------------------+ |        9 | Haskell  |
                         |       10 | Haskell  |
                         |       11 | Haskell  |
                         |       12 | Rust     |
diff --git a/2024/08.rs b/2024/08.rs
new file mode 100644
index 0000000..cf75790 100644
--- /dev/null
+++ a/2024/08.rs
@@ -1,0 +1,65 @@
+use std::collections::{HashMap, HashSet};
+
+#[allow(clippy::cast_possible_wrap)]
+fn main() {
+    let mut frequencies = HashMap::<char, Vec<(i64, i64)>>::new();
+    let mut max_x = 0;
+    let mut max_y = 0;
+
+    for (y, line) in std::io::stdin().lines().enumerate() {
+        for (x, c) in line.unwrap().chars().enumerate() {
+            if c != '.' {
+                frequencies.entry(c).or_default().push((x as i64, y as i64));
+            }
+            max_x = x as i64;
+        }
+        max_y = y as i64;
+    }
+
+    let mut part1 = HashSet::new();
+    let mut part2 = HashSet::new();
+
+    for frequencies in frequencies.values() {
+        for (x1, y1) in frequencies {
+            for (x2, y2) in frequencies {
+                if x1 == x2 && y1 == y2 {
+                    continue;
+                }
+
+                let vx = x2 - x1;
+                let vy = y2 - y1;
+
+                let derive = |out: &mut HashSet<_>, n| {
+                    let mut hit = false;
+
+                    let dx = x1 + n * vx;
+                    let dy = y1 + n * vy;
+                    if dx >= 0 && dx <= max_x && dy >= 0 && dy <= max_y {
+                        out.insert((dx, dy));
+                        hit = true;
+                    }
+
+                    let dx = x2 - n * vx;
+                    let dy = y2 - n * vy;
+                    if dx >= 0 && dx <= max_x && dy >= 0 && dy <= max_y {
+                        out.insert((dx, dy));
+                        hit = true;
+                    }
+
+                    hit
+                };
+
+                derive(&mut part1, 2);
+
+                for i in 0.. {
+                    if !derive(&mut part2, i) {
+                        break;
+                    }
+                }
+            }
+        }
+    }
+
+    eprintln!("{}", part1.len());
+    eprintln!("{}", part2.len());
+}
--
rgit 0.1.5