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|
use nom::{
bytes::complete::tag,
character::complete::{alpha1, anychar, line_ending},
combinator::map,
multi::{many0, separated_list1},
sequence::tuple,
IResult,
};
use std::{collections::BTreeMap, fs};
fn main() -> Result<(), Box<dyn std::error::Error>> {
let input = fs::read_to_string("inputs/day_14.txt")?;
let mut polymer = parse_polymer_expansion(&input).unwrap().1;
let small_expansion_counts = polymer.count_after_expansions(10);
dbg!(small_expansion_counts.most_common() - small_expansion_counts.least_common());
let big_expansion_counts = polymer.count_after_expansions(40);
dbg!(big_expansion_counts.most_common() - big_expansion_counts.least_common());
Ok(())
}
#[derive(Debug)]
struct PolymerExpansion {
polymer: Vec<char>,
rules: Rules,
cache: BTreeMap<(char, char, usize), ElementCount>,
}
impl PolymerExpansion {
fn new(polymer: Vec<char>, rules: Rules) -> PolymerExpansion {
PolymerExpansion {
polymer,
rules,
cache: BTreeMap::new(),
}
}
fn count_after_expansions(&mut self, expansions: usize) -> ElementCount {
let mut counts = ElementCount::default();
for i in 0..self.polymer.len() - 1 {
counts.add(self.polymer[i]);
counts.append(self.count_between(self.polymer[i], self.polymer[i + 1], expansions));
}
counts.add(self.polymer[self.polymer.len() - 1]);
counts
}
fn count_between(
&mut self,
left: char,
right: char,
remaining_expansions: usize,
) -> ElementCount {
if remaining_expansions == 0 {
ElementCount::default()
} else if let Some(cached) = self.cache.get(&(left, right, remaining_expansions)) {
cached.clone()
} else {
let mut counts = ElementCount::default();
let middle = self.rules.get(&[left, right]).expect("No rule!");
counts.add(middle);
counts.append(self.count_between(left, middle, remaining_expansions - 1));
counts.append(self.count_between(middle, right, remaining_expansions - 1));
self.cache
.insert((left, right, remaining_expansions), counts.clone());
counts
}
}
}
#[derive(Debug, Default, Clone)]
struct ElementCount(BTreeMap<char, u64>);
impl ElementCount {
fn add(&mut self, c: char) {
*self.0.entry(c).or_insert(0) += 1;
}
fn append(&mut self, other: ElementCount) {
for (key, val) in other.0 {
*self.0.entry(key).or_insert(0) += val;
}
}
fn most_common(&self) -> u64 {
self.0.values().max().cloned().unwrap_or(0)
}
fn least_common(&self) -> u64 {
self.0.values().min().cloned().unwrap_or(0)
}
}
#[derive(Debug)]
struct Rules {
rules: BTreeMap<[char; 2], char>,
}
impl Rules {
fn get(&self, key: &[char; 2]) -> Option<char> {
self.rules.get(key).cloned()
}
}
fn parse_polymer_expansion(input: &str) -> IResult<&str, PolymerExpansion> {
let (input, polymer) = map(alpha1, |s: &str| s.chars().collect())(input)?;
let (input, _) = many0(line_ending)(input)?;
let (input, rules) = parse_rules(input)?;
Ok((input, PolymerExpansion::new(polymer, rules)))
}
fn parse_rules(input: &str) -> IResult<&str, Rules> {
map(separated_list1(line_ending, parse_rule), |rules| Rules {
rules: rules.into_iter().collect(),
})(input)
}
fn parse_rule(input: &str) -> IResult<&str, ([char; 2], char)> {
map(
tuple((anychar, anychar, tag(" -> "), anychar)),
|(p1, p2, _, r)| ([p1, p2], r),
)(input)
}
|
