year2020/
day03.rs

1use utils::geometry::Vec2;
2use utils::grid;
3use utils::prelude::*;
4
5/// Counting obstacles on slopes through a repeating grid.
6#[derive(Clone, Debug)]
7pub struct Day03 {
8    part1: u64,
9    part2: u64,
10}
11
12const SLOPES: [Vec2<usize>; 5] = [
13    Vec2::new(1, 1),
14    Vec2::new(3, 1),
15    Vec2::new(5, 1),
16    Vec2::new(7, 1),
17    Vec2::new(1, 2),
18];
19
20impl Day03 {
21    pub fn new(input: &str, _: InputType) -> Result<Self, InputError> {
22        let mut counts = [0; SLOPES.len()];
23        grid::for_each_row(
24            input,
25            |b| matches!(b, b'.' | b'#'),
26            || "expected '.' or '#'",
27            |row, cols, trees| {
28                for (delta, count) in SLOPES.into_iter().zip(counts.iter_mut()) {
29                    if row.is_multiple_of(delta.y) {
30                        let col = ((row / delta.y) * delta.x) % cols;
31                        *count += u64::from(trees[col] == b'#');
32                    }
33                }
34                Ok(())
35            },
36        )?;
37
38        Ok(Self {
39            part1: counts[1],
40            part2: counts.iter().product(),
41        })
42    }
43
44    #[must_use]
45    pub fn part1(&self) -> u64 {
46        self.part1
47    }
48
49    #[must_use]
50    pub fn part2(&self) -> u64 {
51        self.part2
52    }
53}
54
55examples!(Day03 -> (u64, u64) [
56    {file: "day03_example0.txt", part1: 7, part2: 336},
57]);
year2020/day03.rs

year2020/
day03.rs
