Days 1-5

src/4-printing-department.rs

@@ -0,0 +1,64 @@
+use std::{fs::File, io::{self, BufRead, BufReader}};
+
+const NEIGHBOURS: [(i32, i32); 8] = [
+    (-1, -1), (0, -1), (1, -1),
+    (-1,  0),          (1,  0),
+    (-1,  1), (0,  1), (1,  1),
+];
+
+fn get_grid_cell(grid: &[Vec<bool>], x: i32, y: i32) -> bool {
+    let (Ok(ux), Ok(uy)) = (usize::try_from(x), usize::try_from(y)) else {
+        return false
+    };
+    grid.get(uy)
+        .and_then(|row| row.get(ux))
+        .copied()
+        .unwrap_or(false)
+}
+
+fn count_surrounding(grid: &[Vec<bool>], x: i32, y: i32) -> i32 {
+    NEIGHBOURS
+    .iter()
+    .map(|(dx, dy)| get_grid_cell(grid, x + dx, y + dy))
+    .filter(|&p| p)
+    .count() as i32
+}
+
+fn update_grid(grid: &[Vec<bool>]) -> Vec<Vec<bool>> {
+    let height = grid.len();
+    let width = grid[0].len();
+    (0..height).map(|y| {
+        (0..width).map(|x| {
+            let x = x as i32;
+            let y = y as i32;
+            get_grid_cell(grid, x, y) && (count_surrounding(grid, x, y) >= 4)
+        }).collect::<Vec<_>>()
+    }).collect::<Vec<_>>()
+}
+
+fn count_all_true(grid: &[Vec<bool>]) -> usize {
+    grid.iter().flatten().filter(|&&b| b).count()
+}
+
+fn main() -> Result<(), io::Error> {
+    let f = File::open("4-input.txt")?;
+    let reader = BufReader::new(f);
+    let original_grid = reader
+        .lines()
+        .collect::<Result<Vec<_>, _>>()?
+        .iter()
+        .map(|s| s.chars().map(|c| c == '@').collect::<Vec<_>>())
+        .collect::<Vec<_>>();
+
+    let mut last_grid = original_grid.clone();
+    loop {
+        let next_grid = update_grid(&last_grid);
+        if next_grid == last_grid {
+            break;
+        }
+        last_grid = next_grid;
+    }
+
+    println!("Result: {}", count_all_true(&original_grid) - count_all_true(&last_grid));
+    Ok(())
+}