aoc2016/src/days/d14.rs

use crate::prelude::*;

pub type O = usize;

pub const INPUT: &'static str = "qzyelonm";

fn _solve (extra: u32) -> O {
    let mut candidates: M<char, Vec<usize>> = M::new();
    let mut done: Vec<usize> = vec![];

    for i in 0.. {
        let s = format!("{INPUT}{i}");
        let mut hash = md5::compute(s);
        let mut repr = format!("{:x}", hash);

        for _ in 0..extra {
            hash = md5::compute(repr);
            repr = format!("{:x}", hash);
        }

        let three = repr.chars().tuple_windows().find(|&(a, b, c)| a == b && b == c);

        if let Some((c, _, _)) = three {
            if !candidates.is_empty() {
                let five = repr.chars().tuple_windows().find(|&(a, b, c, d, e)| a == b && a == c && a == d && a == e);
                if let Some((c, _, _, _, _)) = five {
                    if let Some(candidates) = candidates.get_mut(&c) {
                        let pos = candidates.iter().position(|pos| pos + 1000 > i);
                        if let Some(pos) = pos {
                            done.extend(candidates.drain(pos..));
                            candidates.clear();
                            if done.len() >= 100 { // should be pretty solid, but not sure if I can prove this!
                                done.sort();
                                return done[63];
                            }
                        }
                    }

                }
            }
            candidates.entry(c).or_default().push(i);
        }
    }
    0
}

fn _silver () -> O {
    _solve(0)
}

fn _gold () -> O {
    _solve(2016)
}

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

    #[test]
    fn silver () {
        let ans = _silver();

        assert_eq!(ans, 15168)
    }

    #[test]
    fn gold () {
        let ans = _gold();

        assert_eq!(ans, 20864)
    }
}