day6.rs

// https://adventofcode.com/2019/day/6
// https://doc.rust-lang.org/beta/std/collections/struct.HashMap.html
use std::fs;
use std::collections::{
    HashSet, HashMap, VecDeque
};

fn main() {
    let mut graph = HashMap::new();
    let mut reachable = HashMap::new();
    // let input = fs::read_to_string("./src/6.example").unwrap();
    let input = fs::read_to_string("./src/6.input").unwrap();
    for line in input.lines() {
        let x = line.split(")").collect::<Vec<&str>>();
        let (from, to) = (x[0], x[1]);
        
        if let None = graph.get(&from) {
           graph.insert(from, HashSet::new()); 
           reachable.insert(from, HashSet::new()); 
        }
        let orbit = graph.get_mut(&from).unwrap();
        orbit.insert(to);
        let orbit = reachable.get_mut(&from).unwrap();
        orbit.insert(to);
    }
    // println!("{:?}\n", graph);
    for base_planet in graph.clone().keys() {
        let mut next = VecDeque::new();
        let y = graph.get_mut(base_planet).unwrap().clone();
        for p in y.iter() {
            next.push_front(p);
        }

        while !next.is_empty() {
            let planet = next.pop_front().unwrap();
            let planets = graph.get(planet);
            if let Some(orbiting_planets) = planets {
                for orbiting_planet in orbiting_planets.iter() {
                    next.push_back(orbiting_planet);
                    reachable.get_mut(base_planet).unwrap().insert(orbiting_planet);
                }
            }
        }
    }
    let answer: usize = reachable.values().map(|planets| planets.len()).sum();
    println!("answer: {:?}", answer);
}