advent-of-code/2021/src/bin/day06.rs

#![feature(test)]
extern crate test;
use aoc2021::common::*;

const DAY: usize = 6;
const FERTILITY_CYCLE: usize = 7;
const DAYS_TO_FERTILITY: usize = 2;
type Parsed = Vec<usize>;

fn parse_input(raw: &str) -> Parsed {
    parse_nums_comma(raw)
}

fn simulate<const LIMIT: usize>(parsed: &Parsed) -> usize {
    let mut fish_from_day = [1; LIMIT];
    for i in (0..LIMIT).rev() {
        let mut next_child = i + FERTILITY_CYCLE + DAYS_TO_FERTILITY;
        while next_child < LIMIT {
            fish_from_day[i] += fish_from_day[next_child];
            next_child += FERTILITY_CYCLE;
        }
    }
    let adult_from_day: Vec<usize> = (0..FERTILITY_CYCLE)
        .map(|i| std::iter::successors(Some(i), |i| Some(i + FERTILITY_CYCLE).filter(|i| i < &LIMIT)).map(|i| fish_from_day[i]).sum())
        .collect();
    parsed.iter().map(|&i| 1 + adult_from_day[i]).sum()
}

fn main() {
    let input = parse_input(&read_file(DAY));
    println!("Part 1: {}", simulate::<80>(&input));
    println!("Part 2: {}", simulate::<256>(&input));
}

#[cfg(test)]
mod tests {
    use super::*;
    use aoc2021::*;

    const TEST_INPUT: &str = "3,4,3,1,2";

    test!(simulate<80>() == 5934);
    test!(simulate<256>() == 26984457539);
    bench!(simulate<80>() == 365862);
    bench!(simulate<256>() == 1653250886439);
    bench_input!(Vec::len => 300);
}