25.rs

use std::collections::{HashMap, HashSet};
advent_of_code::solution!(25);

pub fn part_one(input: &str) -> Option<usize> {
    let mut G: HashMap<&str, HashSet<&str>> = HashMap::new();
    input.lines().for_each(|line| {
        let mut parts = line.split(": ");
        let a = parts.next().unwrap();
        let b = parts.next().unwrap().split(" ");
        for c in b {
            G.entry(a).or_insert(HashSet::new()).insert(c);
            G.entry(c).or_insert(HashSet::new()).insert(a);
        }

    });
    let mut S: HashSet<&str> = G.keys().cloned().collect();
    let G_keys: HashSet<&str> = G.keys().cloned().collect();

    while S.iter().map(|&v| G[v].difference(&S).count()).sum::<usize>() != 3 {
        let &max_v = S.iter().max_by_key(|&&v| G[v].difference(&S).count()).unwrap();
        S.remove(max_v);
    }

    Some(S.len() * (G_keys.difference(&S).count()))
}

pub fn part_two(input: &str) -> Option<u32> {
    None
}

#[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(54));
    }

    #[test]
    fn test_part_two() {
        let result = part_two(&advent_of_code::template::read_file("examples", DAY));
        assert_eq!(result, None);
    }
}