01.rs

advent_of_code::solution!(1);

pub fn part_one(input: &str) -> Option<u32> {
    Some(
        input
            .lines()
            .filter_map(|line| {
                let mut nums = line.chars().filter_map(|ch| ch.to_digit(10));
                let first = nums.next();
                let last = nums.next_back().or(first);
                first.zip(last).map(|(a, b)| a * 10 + b)
            })
            .sum(),
    )
}

pub fn part_two(input: &str) -> Option<u32> {
    let digit_strs = [
        ("one", 1u32),
        ("two", 2),
        ("three", 3),
        ("four", 4),
        ("five", 5),
        ("six", 6),
        ("seven", 7),
        ("eight", 8),
        ("nine", 9),
        ("1", 1),
        ("2", 2),
        ("3", 3),
        ("4", 4),
        ("5", 5),
        ("6", 6),
        ("7", 7),
        ("8", 8),
        ("9", 9),
    ];
    Some(
        input
            .lines()
            .filter_map(|line| {
                let first = (0..line.len()).find_map(|start| {
                    digit_strs.iter().find_map(|&(digit_str, val)| {
                        if line[start..].starts_with(digit_str) {
                            Some(val)
                        } else {
                            None
                        }
                    })
                });
                let last = (0..line.len()).rev().find_map(|end| {
                    digit_strs.iter().find_map(|&(digit_str, val)| {
                        if line[..=end].ends_with(digit_str) {
                            Some(val)
                        } else {
                            None
                        }
                    })
                });
                first.zip(last).map(|(a, b)| a * 10 + b)
            })
            .sum(),
    )
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_part_one() {
        let result = part_one(&advent_of_code::template::read_file("examples", DAY));
        assert_eq!(result, Some(142));
    }

    #[test]
    fn test_part_two() {
        let result = part_two(&advent_of_code::template::read_file_part(
            "examples", DAY, 2,
        ));
        assert_eq!(result, Some(281));
    }
}