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use std::collections::HashMap;
fn main() {
let input : Vec<u32> = advent::read_file(6).trim_end()
.split_terminator(',')
.map(|n| n.parse::<u32>().unwrap())
.collect();
println!("6a: {}", simulate(&input, 80));
println!("6b: {}", simulate(&input, 256));
}
fn simulate(input: &[u32], days: u32) -> usize {
let mut fish = HashMap::new();
for days in 0 ..= 8 {
fish.insert(days, 0);
}
for f in input {
let count = fish.entry(*f).or_insert(0);
*count += 1;
}
for _ in 0 .. days {
let mut new_fish = HashMap::new();
for remaining in 1 ..= 8 {
new_fish.insert(remaining - 1, *fish.get(&remaining).unwrap());
}
new_fish.insert(8, *fish.get(&0).unwrap());
let count = new_fish.entry(6).or_insert(0);
*count += fish.get(&0).unwrap();
fish = new_fish;
}
fish.values().sum()
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn test() {
let input = [3,4,3,1,2];
assert_eq!(simulate(&input, 18), 26);
assert_eq!(simulate(&input, 80), 5934);
}
}
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