advent: add helper image class (not currently used).

src/image.rs

@@ -0,0 +1,95 @@
+use crate::prelude::*;
+
+pub struct Image {
+    width: usize,
+    height: usize,
+    pixels: Vec<u8>,
+}
+
+impl Image {
+    fn kernel3x3<F>(&mut self, (x, y): (usize, usize), func: F)
+    where
+        F: Fn(u8) -> u8,
+    {
+        if x > 0 {
+            self[(x - 1, y)] = func(self[(x - 1, y)]);
+            if y > 0 {
+                self[(x - 1, y - 1)] = func(self[(x - 1, y - 1)]);
+            }
+            if y < self.height - 1 {
+                self[(x - 1, y + 1)] = func(self[(x - 1, y + 1)]);
+            }
+        }
+
+        if y > 0 {
+            self[(x, y - 1)] = func(self[(x, y - 1)]);
+        }
+        self[(x, y)] = func(self[(x, y)]);
+        if y < self.height - 1 {
+            self[(x, y + 1)] = func(self[(x, y + 1)]);
+        }
+
+        if x < self.width - 1 {
+            self[(x + 1, y)] = func(self[(x + 1, y)]);
+            if y > 0 {
+                self[(x + 1, y - 1)] = func(self[(x + 1, y - 1)]);
+            }
+            if y < self.height - 1 {
+                self[(x + 1, y + 1)] = func(self[(x + 1, y + 1)]);
+            }
+        }
+    }
+}
+
+impl PartialEq for Image {
+    fn eq(&self, other: &Self) -> bool {
+        self.width == other.width && self.height == other.height && self.pixels == other.pixels
+    }
+}
+
+impl Debug for Image {
+    fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error> {
+        writeln!(f)?;
+        for y in 0..self.height {
+            for x in 0..self.width {
+                write!(f, "{:2}", self[(x, y)] as char)?;
+            }
+            writeln!(f)?;
+        }
+        Ok(())
+    }
+}
+
+impl FromStr for Image {
+    type Err = Infallible;
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        let rows: Vec<_> = s.lines().collect();
+        let width = rows[0].len();
+        let height = rows.len();
+        let pixels = rows
+            .iter()
+            .flat_map(|row| row.as_bytes().iter())
+            .map(|b| *b)
+            .collect();
+
+        Ok(Image {
+            width,
+            height,
+            pixels,
+        })
+    }
+}
+
+impl Index<(usize, usize)> for Image {
+    type Output = u8;
+    fn index(&self, (x, y): (usize, usize)) -> &Self::Output {
+        &self.pixels[x + y * self.width]
+    }
+}
+
+impl IndexMut<(usize, usize)> for Image {
+    fn index_mut(&mut self, (x, y): (usize, usize)) -> &mut Self::Output {
+        &mut self.pixels[x + y * self.width]
+    }
+}

src/lib.rs

@@ -1,5 +1,6 @@
 pub mod prelude {
     pub use std::{
+        collections::{HashMap, HashSet},
         convert::Infallible,
         fmt::{Debug, Display, Error, Formatter},
         io::Read,
@@ -10,4 +11,8 @@ pub mod prelude {
 
     pub use anyhow::Result;
     pub use thiserror::Error;
+
+    pub use crate::image::Image;
 }
+
+mod image;