AdventOfCode2025/src/solutions/day07.rs

use super::Solution;

pub struct Day07 {}

impl Solution for Day07 {
    fn part1(
        &self,
        input: &mut Vec<String>,
    ) -> Result<Box<dyn std::fmt::Display>, Box<dyn std::error::Error>> {
        let (p1, _p2) = self.solve_paths(input);
        Ok(Box::new(p1))
    }

    fn part2(
        &self,
        input: &mut Vec<String>,
    ) -> Result<Box<dyn std::fmt::Display>, Box<dyn std::error::Error>> {
        let (_p1, p2) = self.solve_paths(input);
        Ok(Box::new(p2))
    }

    fn get_day(&self) -> u8 {
        7
    }
}

impl Day07 {
    fn solve_paths(&self, input: &Vec<String>) -> (usize, usize) {
        let lines: Vec<_> = input.iter().map(String::as_bytes).collect();
        let width = lines[0].len();
        let start = lines[0].iter().position(|&b| b == b'S').unwrap();

        let mut splits = 0;
        let mut current = vec![0; width];
        let mut next = vec![0; width];

        current[start] = 1;

        for row in lines {
            for (i, &count) in current.iter().enumerate() {
                if count > 0 {
                    if row[i] == b'^' {
                        splits += 1;

                        if i > 0 {
                            next[i - 1] += count;
                        }
                        if i < width - 1 {
                            next[i + 1] += count;
                        }
                    } else {
                        next[i] += count;
                    }
                }
            }

            (current, next) = (next, current);
            next.fill(0);
        }

        (splits, current.iter().sum())
    }
}

/// Test from puzzle input
#[cfg(test)]
mod test {
    use super::*;
    use crate::*;

    #[test]
    fn part1() {
        let challenge = day07::Day07 {};

        //Complete the Challenge
        let answer = challenge
            .part1(
                utils::get_input(challenge.get_day(), utils::InputType::Test1)
                    .unwrap()
                    .as_mut(),
            )
            .unwrap()
            .to_string();

        assert_eq!(answer, "21");
    }

    #[test]
    fn part2() {
        let challenge = day07::Day07 {};

        //Complete the Challenge
        let answer = challenge
            .part2(
                utils::get_input(challenge.get_day(), utils::InputType::Test2)
                    .unwrap()
                    .as_mut(),
            )
            .unwrap()
            .to_string();

        assert_eq!(answer, "40");
    }
}