aoc/year2025/
day04.rs

1//! # Printing Department
2use crate::util::grid::*;
3use crate::util::point::*;
4
5type Input = (Vec<Point>, Grid<u8>);
6
7pub fn parse(input: &str) -> Input {
8    let grid = Grid::parse(input);
9    let offset = Point::new(1, 1);
10    let mut todo = Vec::new();
11    let mut padded = Grid::new(grid.width + 2, grid.height + 2, u8::MAX);
12
13    for y in 0..grid.height {
14        for x in 0..grid.width {
15            let point = Point::new(x, y);
16
17            if grid[point] == b'@' {
18                let count = DIAGONAL
19                    .iter()
20                    .map(|&d| point + d)
21                    .filter(|&next| grid.contains(next) && grid[next] == b'@')
22                    .count();
23
24                if count < 4 {
25                    todo.push(point + offset);
26                }
27                padded[point + offset] = count as u8;
28            }
29        }
30    }
31
32    (todo, padded)
33}
34
35pub fn part1(input: &Input) -> usize {
36    let (todo, _) = input;
37    todo.len()
38}
39
40pub fn part2(input: &Input) -> usize {
41    let (mut todo, mut padded) = input.clone();
42    let mut removed = 0;
43
44    while let Some(point) = todo.pop() {
45        removed += 1;
46
47        for next in DIAGONAL.map(|d| point + d) {
48            if padded[next] == 4 {
49                todo.push(next);
50            }
51            padded[next] -= 1;
52        }
53    }
54
55    removed
56}
aoc/year2025/day04.rs

aoc/year2025/
day04.rs
