year2024/
day04.rs

1use utils::grid;
2use utils::prelude::*;
3
4/// Counting matches in a word search.
5#[derive(Clone, Debug)]
6pub struct Day04 {
7    cols: usize,
8    grid: Vec<u8>,
9}
10
11impl Day04 {
12    pub fn new(input: &str, _: InputType) -> Result<Self, InputError> {
13        let (_, cols, grid) = grid::parse(
14            input,
15            3,
16            0,
17            |b| b,
18            |b| matches!(b, b'X' | b'M' | b'A' | b'S'),
19            |_, _| Err("expected 'X', 'M', 'A', 'S'"),
20        )?;
21        Ok(Self { cols, grid })
22    }
23
24    #[must_use]
25    pub fn part1(&self) -> u32 {
26        self.check_offset(self.cols as isize)
27            + self.check_offset(-(self.cols as isize))
28            + self.check_offset(1)
29            + self.check_offset(-1)
30            + self.check_offset((self.cols as isize) + 1)
31            + self.check_offset((self.cols as isize) - 1)
32            + self.check_offset(-(self.cols as isize) + 1)
33            + self.check_offset(-(self.cols as isize) - 1)
34    }
35
36    fn check_offset(&self, offset: isize) -> u32 {
37        let start = 3 * self.cols + 3;
38        let mut count = 0;
39        for (((first, second), third), fourth) in self.grid[start..]
40            .iter()
41            .zip(&self.grid[start.wrapping_add_signed(offset)..])
42            .zip(&self.grid[start.wrapping_add_signed(offset * 2)..])
43            .zip(&self.grid[start.wrapping_add_signed(offset * 3)..])
44        {
45            count += u32::from(
46                (*first == b'X') & (*second == b'M') & (*third == b'A') & (*fourth == b'S'),
47            );
48        }
49        count
50    }
51
52    #[must_use]
53    pub fn part2(&self) -> u32 {
54        let mut count = 0;
55        for ((((middle, nw), ne), sw), se) in self.grid[self.cols * 4 + 4..]
56            .iter()
57            .zip(&self.grid[self.cols * 3 + 3..])
58            .zip(&self.grid[self.cols * 3 + 5..])
59            .zip(&self.grid[self.cols * 5 + 3..])
60            .zip(&self.grid[self.cols * 5 + 5..])
61        {
62            count += u32::from(
63                (*middle == b'A') & ((*nw ^ *se) == (b'M' ^ b'S')) & ((*ne ^ *sw) == (b'M' ^ b'S')),
64            );
65        }
66        count
67    }
68}
69
70examples!(Day04 -> (u32, u32) [
71    {file: "day04_example0.txt", part1: 18, part2: 9},
72]);
year2024/day04.rs

year2024/
day04.rs
