adventofcode/2018/src/day05.rs

use std::io::Read;

use common;

#[derive(Default)]
pub struct Day05 {}

impl Day05 {
    pub fn new() -> Day05 {
        Default::default()
    }

    fn reduce(mut data: Vec<u8>) -> usize {
        let mut dptr = 0;
        for iptr in 0..data.len() {
            // This originally had a nice comparison
            // data[iptr] != data[dptr - 1] && data[iptr].eq_ignore_ascii_case(data[dptr - 1])
            // However this is way faster, and does about the same
            if dptr > 0 && (data[iptr] ^ data[dptr - 1]) == 32 {
                dptr -= 1;
            } else {
                data[dptr] = data[iptr];
                dptr += 1;
            }
        }

        dptr
    }
}

impl common::Solution for Day05 {
    fn part1(&mut self, input: &mut Read) -> String {
        let mut data = Vec::new();
        input.read_to_end(&mut data).expect("Can't read input!");
        common::trim_back(&mut data);

        Day05::reduce(data).to_string()
    }

    fn part2(&mut self, input: &mut Read) -> String {
        let mut data = Vec::new();
        input.read_to_end(&mut data).expect("Can't read input!");
        common::trim_back(&mut data);

        let min_len = (b'a'..=b'z')
            .map(|option| {
                data.iter()
                    .filter(|&x| !x.eq_ignore_ascii_case(&option))
                    .cloned()
                    .collect()
            })
            .map(Day05::reduce)
            .min()
            .unwrap();

        min_len.to_string()
    }
}

#[cfg(test)]
mod tests {
    use common::Solution;
    use day05::Day05;

    const SAMPLE_INPUT: &[u8] = include_bytes!("samples/05.txt");

    #[test]
    fn sample_part1() {
        let mut instance = Day05::new();
        assert_eq!("10", instance.part1(&mut SAMPLE_INPUT));
    }

    #[test]
    fn sample_part2() {
        let mut instance = Day05::new();
        assert_eq!("4", instance.part2(&mut SAMPLE_INPUT));
    }
}