2019

day01.rs

const INPUT: &str = include_str!("../input");

fn parse(s: &str) -> Vec<u32> {
    s.lines().map(|x| x.parse().unwrap()).collect()
}

fn required_fuel(st: u32) -> Option<u32> {
    (st / 3).checked_sub(2)
}
fn solve_a(v: &[u32]) -> u32 {
    v.iter().map(|x| required_fuel(*x)).sum::<Option<_>>().unwrap()
}

fn solve_b(v: &[u32]) -> u32 {
    fn calc(st: u32) -> impl Iterator<Item = u32> {
        std::iter::successors(required_fuel(st), |v| required_fuel(*v))
    }   
    v.iter().flat_map(|v| calc(*v)).sum()
}

fn main() {
    let input = parse(INPUT);

    println!("A: {}", solve_a(&input));
    println!("B: {}", solve_b(&input));
}

#[test]
fn test_a() {
    assert_eq!(2, solve_a(&[12]));
    assert_eq!(2, solve_a(&[14]));
    assert_eq!(654, solve_a(&[1969]));
    assert_eq!(33583, solve_a(&[100756]));
}   

#[test]
fn test_b() {
    assert_eq!(2, solve_b(&[12]));
    assert_eq!(966, solve_b(&[1969]));
    assert_eq!(50346, solve_b(&[100756]));
}