adventofcode day6 part2

day6.rs

use std::collections::HashMap;

static DATA: &str = "3,5,1,2,5,4,1,5,1,2,5,5,1,3,1,5,1,3,2,1,5,1,1,1,2,3,1,3,1,2,1,1,5,1,5,4,5,5,3,3,1,5,1,1,5,5,1,3,5,5,3,2,2,4,1,5,3,4,2,5,4,1,2,2,5,1,1,2,4,4,1,3,1,3,1,1,2,2,1,1,5,1,1,4,4,5,5,1,2,1,4,1,1,4,4,3,4,2,2,3,3,2,1,3,3,2,1,1,1,2,1,4,2,2,1,5,5,3,4,5,5,2,5,2,2,5,3,3,1,2,4,2,1,5,1,1,2,3,5,5,1,1,5,5,1,4,5,3,5,2,3,2,4,3,1,4,2,5,1,3,2,1,1,3,4,2,1,1,1,1,2,1,4,3,1,3,1,2,4,1,2,4,3,2,3,5,5,3,3,1,2,3,4,5,2,4,5,1,1,1,4,5,3,5,3,5,1,1,5,1,5,3,1,2,3,4,1,1,4,1,2,4,1,5,4,1,5,4,2,1,5,2,1,3,5,5,4,5,5,1,1,4,1,2,3,5,3,3,1,1,1,4,3,1,1,4,1,5,3,5,1,4,2,5,1,1,4,4,4,2,5,1,2,5,2,1,3,1,5,1,2,1,1,5,2,4,2,1,3,5,5,4,1,1,1,5,5,2,1,1";

fn main() {
    let input: Vec<i8> = DATA.split(",").map(|x| x.parse::<i8>().unwrap()).collect();
    let mut fish_per_day_map: HashMap<i8, i64> = HashMap::new();

    for day in input {
        *fish_per_day_map.entry(day).or_insert(0) += 1;
    }

    let mut counter = 0;

    while counter < 256 {
        let mut new_ones: HashMap<i8, i64> = HashMap::new();

        for (&key, _) in &fish_per_day_map {
            new_ones.entry(key).or_insert(0);
            let number_of_fish_to_add = fish_per_day_map.get(&key).unwrap();
            if key == 0 {
                *new_ones.entry(6).or_insert(0) += *number_of_fish_to_add;
                *new_ones.entry(8).or_insert(0) += *number_of_fish_to_add;
            } else {
                *new_ones.entry(key - 1).or_insert(0) += *number_of_fish_to_add;
            }
        }
        counter += 1;
        fish_per_day_map = new_ones
    }

    let mut total: i64 = 0;

    for value in fish_per_day_map.values() {
        total += value
    }
    println!("{}", total);
}