advent-of-code/aoc2015/src/day04.rs

use std::fmt::Write;

use md5::{Digest, Md5};

use anyhow::{anyhow, Result};

const INPUT: &str = include_str!("../input/day04.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<u64> {
    let input = input.trim_end();
    let mut content = String::from(input);

    let mut hasher = Md5::new();

    for i in 0.. {
        content.truncate(input.len());
        content.push_str(&i.to_string());

        hasher.input(&content);
        let res = hasher.result_reset();
        if res[..2] == [0, 0] && res[2] <= 0x0f {
            return Ok(i);
        }
    }

    Err(anyhow!("couldn't find a suitable number"))
}

fn part2(input: &str) -> Result<u64> {
    let input = input.trim_end();
    let mut content = String::from(input);

    let mut hasher = Md5::new();

    for i in 0.. {
        content.truncate(input.len());
        content.push_str(&i.to_string());

        hasher.input(&content);
        let res = hasher.result_reset();
        if res[..3] == [0, 0, 0] {
            return Ok(i);
        }
    }

    Err(anyhow!("couldn't find a suitable number"))
}

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

    #[test]
    #[ignore] // takes too long!
    fn part1_provided() {
        assert_eq!(part1("abcdef").unwrap(), 609043);
        assert_eq!(part1("pqrstuv").unwrap(), 1048970);
    }

    #[test]
    #[ignore] // takes too long!
    fn part1_real() {
        assert_eq!(part1(INPUT).unwrap(), 282749);
    }

    #[test]
    #[ignore] // takes too long!
    fn part2_real() {
        assert_eq!(part2(INPUT).unwrap(), 9962624);
    }
}