Day 8

src/day8.rs

@@ -0,0 +1,57 @@
+use itertools::Itertools;
+use std::collections::HashMap;
+
+const EXTEND: bool = true;
+
+pub fn day8() {
+    let (antennae, width, height) = input();
+
+    let mut antinodes: Vec<(i64, i64)> = antennae
+        .values()
+        .flat_map(|antennae_set| {
+            antennae_set
+                .iter()
+                .combinations(2)
+                .flat_map(|pair| {
+                    let ((x1, y1), (x2, y2)) = (pair[0], pair[1]);
+                    let (dx, dy) = (x2 - x1, y2 - y1);
+
+                    if EXTEND {
+                        (0..width.max(height))
+                            .flat_map(|i| [(x1 - dx * i, y1 - dy * i), (x1 + dx * i, y1 + dy * i)])
+                            .collect()
+                    } else {
+                        vec![(x1 - dx, y1 - dy), (x2 + dx, y2 + dy)]
+                    }
+                })
+                .collect::<Vec<(i64, i64)>>()
+        })
+        .filter(|(x, y)| *x < width && *y < height && *x >= 0 && *y >= 0)
+        .collect();
+    antinodes.sort();
+    antinodes.dedup();
+
+    println!("Unique Antinodes: {}", antinodes.len());
+}
+
+fn input() -> (HashMap<char, Vec<(i64, i64)>>, i64, i64) {
+    let input = crate::input(8);
+
+    let unsorted_antennae = input.lines().enumerate().flat_map(|(y, line)| {
+        line.chars()
+            .enumerate()
+            .filter(|(_, c)| *c != '.')
+            .map(move |(x, c)| (c, (x as i64, y as i64)))
+    });
+
+    let mut antennae = HashMap::<char, Vec<(i64, i64)>>::new();
+    for (c, p) in unsorted_antennae {
+        antennae.entry(c).or_default().push(p);
+    }
+
+    (
+        antennae,
+        input.lines().nth(0).unwrap().len() as i64,
+        input.lines().count() as i64,
+    )
+}

src/main.rs

@@ -10,10 +10,12 @@ mod day4;
 mod day5;
 #[allow(dead_code)]
 mod day6;
+#[allow(dead_code)]
 mod day7;
+mod day8;
 
 fn main() {
-    day7::day7();
+    day8::day8();
 }
 
 pub fn input(day: u8) -> String {