advent-of-code/aoc2021/src/day01.rs

use std::fmt::Write;

use anyhow::Result;

const INPUT: &str = include_str!("../input/day01.txt");

pub fn run() -> Result<String> {
    let mut res = String::with_capacity(128);

    writeln!(res, "part 1: {}", part1(INPUT)?)?;
    writeln!(res, "part 2: {}", part2(INPUT)?)?;

    Ok(res)
}

fn part1(input: &str) -> Result<usize> {
    let measurements = input
        .lines()
        .map(|line| line.parse::<u64>().map_err(anyhow::Error::new))
        .collect::<Result<Vec<_>>>()?;

    Ok(count_increases(measurements.iter()))
}

fn count_increases<I, C>(numbers: I) -> usize
where
    C: std::cmp::PartialOrd,
    I: Iterator<Item = C> + Clone,
{
    numbers
        .clone()
        .zip(numbers.skip(1))
        .filter(|(a, b)| a < b)
        .count()
}

fn part2(input: &str) -> Result<usize> {
    let measurements = input
        .lines()
        .map(|line| line.parse::<u64>().map_err(anyhow::Error::new))
        .collect::<Result<Vec<_>>>()?;

    Ok(count_increases(
        measurements.windows(3).map(|w| w.iter().sum::<u64>()),
    ))
}

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

    const PROVIDED: &str = include_str!("../input/day01_provided.txt");

    #[test]
    fn part1_provided() {
        assert_eq!(part1(PROVIDED).unwrap(), 7);
    }

    #[test]
    fn part1_real() {
        assert_eq!(part1(INPUT).unwrap(), 1502);
    }

    #[test]
    fn part2_provided() {
        assert_eq!(part2(PROVIDED).unwrap(), 5);
    }

    #[test]
    fn part2_real() {
        assert_eq!(part2(INPUT).unwrap(), 1538);
    }
}