78 lines
1.7 KiB
Rust
78 lines
1.7 KiB
Rust
//! Day 06 of 2021.
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use crate::prelude::*;
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/// Shorthand for a [`HashMap`] using [`isize`]s.
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type FishMap = HashMap<isize, isize>;
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/// Get the solution for day 06 of 2021.
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pub fn solution() -> Solution {
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Solution::new(Day::new(6, 2021), part_1, part_2)
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.with_expected(343441, 1569108373832_i64)
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}
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/// The logic to solve part one.
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fn part_1(input: &str) -> Result<String> {
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let mut fishes = parse_fishes(input)?;
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for _ in 0..80 {
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fishes = simulate_fishes(fishes);
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}
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Ok(count_fishes(fishes).to_string())
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}
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/// The logic to solve part two.
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fn part_2(input: &str) -> Result<String> {
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let mut fishes = parse_fishes(input)?;
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for _ in 0..256 {
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fishes = simulate_fishes(fishes);
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}
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Ok(count_fishes(fishes).to_string())
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}
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/// Parse the [`FishMap`]s from the puzzle input.
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fn parse_fishes(input: &str) -> Result<FishMap> {
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let mut fishes = FishMap::new();
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let individual_fishes = input
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.split(',')
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.map(str::parse)
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.collect::<Result<Vec<_>, _>>()?;
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for fish in individual_fishes {
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let amount = fishes.entry(fish).or_default();
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*amount += 1;
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}
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Ok(fishes)
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}
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/// Get the sum of the [`FishMap`] values.
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fn count_fishes(fishes: FishMap) -> isize {
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fishes.values().sum()
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}
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/// Simulate the fishes according to the puzzle's instructions.
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fn simulate_fishes(fishes: FishMap) -> FishMap {
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let mut new_fishes = HashMap::new();
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for (mut timer, amount) in fishes {
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timer -= 1;
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if timer < 0 {
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let new_fish = new_fishes.entry(8).or_default();
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*new_fish += amount;
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let reset_fish = new_fishes.entry(6).or_default();
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*reset_fish += amount;
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} else {
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let current_fish = new_fishes.entry(timer).or_default();
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*current_fish += amount;
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}
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}
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new_fishes
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}
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