Day 4

1 files changed, 121 insertions, 0 deletions

diff --git a/src/bin/4.rs b/src/bin/4.rs
new file mode 100644
index 0000000..6fddcd6
--- /dev/null
+++ b/src/bin/4.rs
@@ -0,0 +1,121 @@
+use std::{
+    error::Error,
+    fs,
+    ops::{Add, Mul},
+};
+
+#[derive(Debug, PartialEq, Eq, Copy, Clone)]
+struct Point {
+    pub x: i64,
+    pub y: i64,
+}
+
+impl Point {
+    fn new(x: i64, y: i64) -> Self {
+        Self { x, y }
+    }
+}
+
+impl Mul<i64> for Point {
+    type Output = Self;
+    fn mul(self, rhs: i64) -> Self::Output {
+        Point {
+            x: self.x * rhs,
+            y: self.y * rhs,
+        }
+    }
+}
+
+impl Add<Point> for Point {
+    type Output = Self;
+    fn add(self, rhs: Self) -> Self::Output {
+        Point {
+            x: self.x + rhs.x,
+            y: self.y + rhs.y,
+        }
+    }
+}
+
+#[derive(Debug, PartialEq, Eq, Copy, Clone)]
+enum Dir {
+    North,
+    NorthEast,
+    East,
+    SouthEast,
+    South,
+    SouthWest,
+    West,
+    NorthWest,
+}
+
+impl Dir {
+    const DIRS: [Dir; 8] = [
+        Dir::North,
+        Dir::NorthEast,
+        Dir::East,
+        Dir::SouthEast,
+        Dir::South,
+        Dir::SouthWest,
+        Dir::West,
+        Dir::NorthWest,
+    ];
+    fn grid_offset(self) -> Point {
+        match self {
+            Dir::North => Point::new(0, 1),
+            Dir::NorthEast => Point::new(1, 1),
+            Dir::East => Point::new(1, 0),
+            Dir::SouthEast => Point::new(1, -1),
+            Dir::South => Point::new(0, -1),
+            Dir::SouthWest => Point::new(-1, -1),
+            Dir::West => Point::new(-1, 0),
+            Dir::NorthWest => Point::new(-1, 1),
+        }
+    }
+}
+
+fn index_at(board: &[&[u8]], point: Point) -> Option<u8> {
+    Some(
+        *board
+            .get(usize::try_from(point.y).ok()?)?
+            .get(usize::try_from(point.x).ok()?)?,
+    )
+}
+
+fn main() -> Result<(), Box<dyn Error>> {
+    let mut xmas_count = 0;
+    let mut x_mas_count = 0;
+    let to_find = b"XMAS";
+    let input = fs::read("input/4")?;
+    let input: Box<[&[u8]]> = input.trim_ascii_end().split(|e| *e == b'\n').collect();
+    for y in 0..input.len() {
+        for x in 0..input[y].len() {
+            let p = Point::new(x as i64, y as i64);
+            for d in Dir::DIRS {
+                if to_find
+                    .iter()
+                    .copied()
+                    .enumerate()
+                    .all(|c| index_at(&input, p + d.grid_offset() * c.0 as i64) == Some(c.1))
+                {
+                    xmas_count += 1;
+                }
+            }
+            if input[y][x] == b'A' {
+                let check = |a, b| {
+                    (a == Some(b'M') && b == Some(b'S')) || (a == Some(b'S') && b == Some(b'M'))
+                };
+                if check(
+                    index_at(&input, p + Dir::NorthEast.grid_offset()),
+                    index_at(&input, p + Dir::SouthWest.grid_offset()),
+                ) && check(
+                    index_at(&input, p + Dir::NorthWest.grid_offset()),
+                    index_at(&input, p + Dir::SouthEast.grid_offset()),
+                ) {
+                    x_mas_count += 1;
+                }
+            }
+        }
+    }
+    println!("{xmas_count}\n{x_mas_count}");
+    Ok(())
+}