1 files changed, 98 insertions, 0 deletions
diff --git a/2019/rust/day08/src/main.rs b/2019/rust/day08/src/main.rs
new file mode 100644
index 0000000..232d2c8
--- /dev/null
+++ b/2019/rust/day08/src/main.rs
@@ -0,0 +1,98 @@
+use std::io::{self, BufRead};
+
+fn read_input() -> Vec<u32> {
+    let stdin = io::stdin();
+    let line = stdin.lock().lines().next();
+    line.unwrap().unwrap().trim_start().trim_end().chars()
+         .map(|c| { let d: u32 = c.to_digit(10).unwrap(); d }).collect()
+}
+
+fn split_layers(mut image: Vec<u32>, width: usize, height: usize) -> Vec<Vec<u32>> {
+    let mut layers:Vec<Vec<u32>> = Vec::new();
+
+    for i in (0..image.len()).step_by(width*height) {
+        let mut layer = Vec::new();
+        layer.append(&mut image[i..i+width*height].to_vec());
+        layers.push(layer);
+    }
+
+    layers
+}
+
+fn combine_layers(layers: &Vec<Vec<u32>>, width: usize, height: usize) -> Vec<u32> {
+    let combined:Vec<Vec<u32>> = (0..height).map(|y| {
+        (0..width).map(|x| {
+            layers.iter().fold(2, |i, l| { if i == 2 { l[y*width+x] } else { i } })
+        }).collect()
+    }).collect();
+
+    combined.into_iter().flatten().collect()
+}
+
+fn print_image(image: &Vec<u32>, width: usize, height: usize) {
+    for y in 0..height {
+        for x in 0..width {
+            if image[y*width + x] == 1 {
+                print!("██");
+            } else {
+                print!("  ");
+            }
+        }
+        println!("");
+    }
+}
+
+fn first_puzzle(layers: &Vec<Vec<u32>>) {
+    let number_counts: Vec<(usize, usize, usize)> = layers.iter()
+        .map(|l| l.iter()
+                .fold((0,0,0), |(mut zeros, mut ones, mut twos), n| {
+                    if *n == 0 { zeros +=  1; }
+                    if *n == 1 { ones  +=  1; }
+                    if *n == 2 { twos  +=  1; }
+                    ( zeros, ones, twos )
+                }
+        )).collect();
+
+    let interesting_layer: Option<usize> = number_counts.iter().enumerate().
+        fold((None, None), |(mut best_layer, mut lowest_zero), (l, n)| {
+            match (best_layer, lowest_zero) {
+                (None, None) => {
+                    best_layer = Some(l);
+                    lowest_zero = Some(n.0);
+                },
+                (_, Some(old_lowest)) => {
+                    if n.0 < old_lowest {
+                        best_layer = Some(l);
+                        lowest_zero = Some(n.0);
+                    }
+                },
+                _ => panic!("Invalid internal logic!"),
+            }
+            (best_layer, lowest_zero)
+        }).0;
+
+    match interesting_layer {
+        Some(i_l) => println!("Solution to first puzzle: {}.",
+             number_counts[i_l].1 * number_counts[i_l].2),
+             None => println!("No solution found for first puzzle."),
+    }
+}
+
+fn second_puzzle(layers: &Vec<Vec<u32>>, width: usize, height: usize) {
+    let image = combine_layers(&layers, width, height);
+
+    println!("Solution to second puzzle: ");
+    print_image(&image, width, height);
+}
+
+fn main() {
+    let encoded_image = read_input();
+    let width = 25;
+    let height = 6;
+    assert!(encoded_image.len() % (width * height) == 0, "Image data is corrupt.");
+
+    let layers = split_layers(encoded_image, width, height);
+
+    first_puzzle(&layers);
+    second_puzzle(&layers, width, height);
+}