day10.rs

use crate::solutions::Solution;
use crate::utils::grid::Grid;
use crate::utils::point::Point;
use itertools::Itertools;

pub struct Day10;

impl Solution for Day10 {
    fn part_one(&self, input: &str) -> String {
        self.solve(input, |points| points.into_iter().unique().collect())
    }

    fn part_two(&self, input: &str) -> String {
        self.solve(input, |points| points)
    }
}

impl Day10 {
    fn solve<F>(&self, input: &str, modify_points: F) -> String
    where
        F: Fn(Vec<Point>) -> Vec<Point>,
    {
        let grid = Grid::from_custom(input.trim(), |c| {
            c.to_digit(10).map(|x| x as i16).unwrap_or(-1)
        });

        grid.get_all_positions(&0)
            .iter()
            .map(|&start| self.process_path(&grid, start, &modify_points))
            .sum::<usize>()
            .to_string()
    }

    fn process_path<F>(&self, grid: &Grid<i16>, start: Point, modify_points: &F) -> usize
    where
        F: Fn(Vec<Point>) -> Vec<Point>,
    {
        let mut current_points = vec![start];
        for current in 0..9 {
            let next = current + 1;
            current_points = modify_points(
                current_points
                    .iter()
                    .flat_map(|point| {
                        point.adjacent().into_iter().filter(|next_point| {
                            grid.get_for_point(next_point)
                                .is_some_and(|&value| value == next)
                        })
                    })
                    .collect(),
            );
        }

        current_points.len()
    }
}

#[cfg(test)]
mod tests {
    use crate::solutions::year2024::day10::Day10;
    use crate::solutions::Solution;

    const EXAMPLE_1: &str = r#"..90..9
...1.98
...2..7
6543456
765.987
876....
987...."#;

    const EXAMPLE_2: &str = r#"89010123
78121874
87430965
96549874
45678903
32019012
01329801
10456732"#;

    #[test]
    fn part_one_example_test_1() {
        const FIRST_EXAMPLE: &str = r#"0123
1234
8765
9876"#;
        assert_eq!("1", Day10.part_one(FIRST_EXAMPLE));
    }

    #[test]
    fn part_one_example_test_2() {
        const EXAMPLE: &str = r#"...0...
...1...
...2...
6543456
7.....7
8.....8
9.....9"#;

        assert_eq!("2", Day10.part_one(EXAMPLE));
    }

    #[test]
    fn part_one_example_test_3() {
        assert_eq!("4", Day10.part_one(EXAMPLE_1));
    }

    #[test]
    fn part_one_example_test_4() {
        const EXAMPLE: &str = r#"10..9..
2...8..
3...7..
4567654
...8..3
...9..2
.....01"#;

        assert_eq!("3", Day10.part_one(EXAMPLE));
    }

    #[test]
    fn part_one_example_test_5() {
        assert_eq!("36", Day10.part_one(EXAMPLE_2));
    }

    #[test]
    fn part_two_example_test_1() {
        const EXAMPLE: &str = r#".....0.
..4321.
..5..2.
..6543.
..7..4.
..8765.
..9...."#;

        assert_eq!("3", Day10.part_two(EXAMPLE));
    }

    #[test]
    fn part_two_example_test_2() {
        assert_eq!("13", Day10.part_two(EXAMPLE_1));
    }

    #[test]
    fn part_two_example_test_3() {
        const EXAMPLE: &str = r#"012345
123456
234567
345678
4.6789
56789."#;

        assert_eq!("227", Day10.part_two(EXAMPLE))
    }

    #[test]
    fn part_two_example_test_4() {
        assert_eq!("81", Day10.part_two(EXAMPLE_2));
    }
}