1 files changed, 82 insertions, 0 deletions
diff --git a/aoc/2024/04/rust/src/main.rs b/aoc/2024/04/rust/src/main.rs
new file mode 100644
index 0000000..191e461
--- /dev/null
+++ b/aoc/2024/04/rust/src/main.rs
@@ -0,0 +1,82 @@
+use std::io;
+
+fn main() -> io::Result<()> {
+    let grid = io::stdin()
+        .lines()
+        .flatten()
+        .map(|line| line.chars().collect())
+        .collect::<Vec<Vec<char>>>();
+    let grid = Grid(grid);
+
+    let silver: usize = silver(&grid);
+    let gold: usize = gold(&grid);
+
+    println!("silver: {silver}");
+    println!("gold: {gold}");
+
+    return Ok(());
+}
+
+struct Grid(Vec<Vec<char>>);
+
+impl Grid {
+    fn at(&self, (x, y): (isize, isize)) -> Option<&char> {
+        self.0
+            .get(usize::try_from(y).ok()?)?
+            .get(usize::try_from(x).ok()?)
+    }
+
+    fn check<'a>(
+        &self,
+        (x, y): (isize, isize),
+        mut pat: impl Iterator<Item = &'a ((isize, isize), char)>,
+    ) -> bool {
+        pat.all(|((dx, dy), ch)| self.at((x + dx, y + dy)).is_some_and(|c| c == ch))
+    }
+
+    fn pts(&self) -> impl Iterator<Item = (isize, isize)> + use<'_> {
+        (0..self.0[0].len()).flat_map(|x| (0..self.0.len()).map(move |y| (x as isize, y as isize)))
+    }
+}
+
+fn silver(grid: &Grid) -> usize {
+    let dirs = vec![
+        (-1, -1),
+        (-1, 0),
+        (-1, 1),
+        (0, -1),
+        (0, 1),
+        (1, -1),
+        (1, 0),
+        (1, 1),
+    ];
+
+    let xmases: Vec<Vec<((isize, isize), char)>> = dirs
+        .iter()
+        .map(|(dx, dy)| {
+            (0..4)
+                .map(move |n| (dx * n, dy * n))
+                .zip("XMAS".chars())
+                .collect()
+        })
+        .collect();
+
+    grid.pts()
+        .flat_map(|p| xmases.iter().map(move |xmas| grid.check(p, xmas.iter())))
+        .filter(|p| *p)
+        .count()
+}
+
+fn gold(grid: &Grid) -> usize {
+    let dirs = vec![(-1, -1), (1, -1), (0, 0), (-1, 1), (1, 1)];
+
+    let xmases: Vec<Vec<((isize, isize), char)>> = vec!["MMASS", "SMASM", "SSAMM", "MSAMS"]
+        .iter()
+        .map(|x| dirs.clone().into_iter().zip(x.chars()).collect())
+        .collect();
+
+    grid.pts()
+        .flat_map(|p| xmases.iter().map(move |xmas| grid.check(p, xmas.iter())))
+        .filter(|p| *p)
+        .count()
+}