AoC21/src/day6.rs

42 lines
1.0 KiB
Rust

pub fn day6() {
// let input = "3,4,3,1,2";
let input = include_str!("../input/day6.txt");
let initial_fishes = input
.trim()
.split(",")
.map(|s| s.parse::<usize>().unwrap())
.collect::<Vec<_>>();
count_fishes_after(&initial_fishes, 18);
count_fishes_after(&initial_fishes, 80);
count_fishes_after(&initial_fishes, 256);
}
fn count_fishes_after(initial_fishes: &[usize], days: u32) {
let mut fish_batches = [0_u64; 9];
for f in initial_fishes {
fish_batches[*f] += 1;
}
for _ in 1..=days {
let old_batches = fish_batches;
fish_batches = [0; 9];
for counter in 0..=7 {
fish_batches[counter] = old_batches[counter + 1];
}
// each fish previously at 0 spawns a new fish with counter 8 and resets its counter to 6
fish_batches[8] = old_batches[0];
fish_batches[6] += old_batches[0];
}
println!(
"total fishes after {} days: {}",
days,
fish_batches.iter().sum::<u64>()
);
}