Add day08

Signed-off-by: Alek Ratzloff <alekratz@gmail.com>

day08/.gitignore

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+target/
+*.txt

day08/Cargo.lock

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+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+[[package]]
+name = "day08"
+version = "0.1.0"
+

day08/Cargo.toml

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+[package]
+name = "day08"
+version = "0.1.0"
+authors = ["Alek Ratzloff <alekratz@gmail.com>"]
+edition = "2018"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]

day08/src/main.rs

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+use std::{
+    fmt::{self, Display, Formatter},
+    io::{self, Read},
+};
+
+type Result<T> = std::result::Result<T, Box<dyn std::error::Error>>;
+
+fn get_input_string() -> io::Result<String> {
+    let mut buffer = String::new();
+    io::stdin().read_to_string(&mut buffer)?;
+    Ok(buffer)
+}
+
+#[allow(unused_macros)]
+macro_rules! todo {
+    ($($tt:tt)*) => { unimplemented!($($tt)*) };
+}
+
+fn main() -> Result<()> {
+    let input_string = get_input_string()?;
+    let image = Image::from_str(25, 6, input_string.trim());
+
+    println!("Image has {} layers", image.layers.len());
+
+    part1(&image);
+    part2(&image);
+    Ok(())
+}
+
+fn part1(image: &Image) {
+    let layer = image.layers
+        .iter()
+        .min_by_key(|layer| layer.data.iter().copied().filter(|n| *n == 0).count())
+        .unwrap();
+
+    let ones = layer.data.iter().copied().filter(|n| *n == 1).count();
+    let twos = layer.data.iter().copied().filter(|n| *n == 2).count();
+    println!("Part 1: {} * {} = {}", ones, twos, ones * twos);
+}
+
+fn part2(image: &Image) {
+    println!("Part 2:");
+    println!("{}", image);
+}
+
+#[derive(Debug, Clone)]
+struct Image {
+    width: usize,
+    height: usize,
+    layers: Vec<Layer>,
+}
+
+impl Display for Image {
+    fn fmt(&self, fmt: &mut Formatter) -> fmt::Result {
+        const ANSI_PIXEL: [&'static str; 3] = [
+            "\u{001b}[40m \u{001b}[0m", // black
+            "\u{001b}[47m \u{001b}[0m", // white
+            "\u{001b}[45;1m \u{001b}[0m", // transparent
+        ];
+        let layer_pixels: Vec<&'static str> = self.layers.iter()
+            .rev()
+            .fold(self.layers.last().unwrap().clone(), |acc, this| this.flatten_over(&acc))
+            .data
+            .into_iter()
+            .map(|n| ANSI_PIXEL[n])
+            .collect();
+
+        for px in layer_pixels.as_slice().chunks(self.width) {
+            writeln!(fmt, "{}", px.join(""))?;
+        }
+        Ok(())
+    }
+}
+
+impl Image {
+    pub fn from_str(width: usize, height: usize, text: &str) -> Self {
+        let count = width * height;
+        let mut idx = 0;
+        let mut layers = Vec::new();
+        while idx < text.len() {
+            let layer = Layer::from_str(width, height, &text[idx..]);
+            layers.push(layer);
+            idx += count;
+        }
+        Image { width, height, layers }
+    }
+}
+
+#[derive(Debug, Clone)]
+struct Layer {
+    width: usize,
+    height: usize,
+    data: Vec<usize>,
+}
+
+impl Layer {
+    pub fn from_str(width: usize, height: usize, text: &str) -> Self {
+        let count = width * height;
+        let text = &text[0 .. count];
+
+        let data: Vec<_> = text.chars()
+            .map(|s| (s as usize) - ('0' as usize))
+            .collect();
+        Layer {
+            width,
+            height,
+            data,
+        }
+    }
+
+    pub fn flatten_over(&self, other: &Layer) -> Layer {
+        assert_eq!(self.width, other.width, "mismatched width");
+        assert_eq!(self.height, other.height, "mismatched height");
+
+        let data = self.data.iter().copied().zip(other.data.iter().copied())
+            .map(|(a, b)| match (a, b) {
+                (2, p)
+                | (p, _) => p
+            }).collect();
+        Layer {
+            width: self.width,
+            height: self.height,
+            data,
+        }
+    }
+}