2021: day14: part 1
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102
aoc2021/input/day14.txt
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102
aoc2021/input/day14.txt
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@ -0,0 +1,102 @@
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CKFFSCFSCBCKBPBCSPKP
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NS -> P
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KV -> B
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FV -> S
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BB -> V
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CF -> O
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CK -> N
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BC -> B
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PV -> N
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KO -> C
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CO -> O
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HP -> P
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HO -> P
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OV -> O
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VO -> C
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SP -> P
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BV -> H
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CB -> F
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SF -> H
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ON -> O
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KK -> V
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HC -> N
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FH -> P
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OO -> P
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VC -> F
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VP -> N
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FO -> F
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CP -> C
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SV -> S
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PF -> O
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OF -> H
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BN -> V
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SC -> V
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SB -> O
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NC -> P
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CN -> K
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BP -> O
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PC -> H
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PS -> C
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NB -> K
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VB -> P
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HS -> V
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BO -> K
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NV -> B
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PK -> K
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SN -> H
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OB -> C
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BK -> S
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KH -> P
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BS -> S
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HV -> O
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FN -> F
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FS -> N
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FP -> F
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PO -> B
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NP -> O
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FF -> H
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PN -> K
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HF -> H
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VK -> K
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NF -> K
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PP -> H
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PH -> B
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SK -> P
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HN -> B
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VS -> V
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VN -> N
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KB -> O
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KC -> O
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KP -> C
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OS -> O
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SO -> O
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VH -> C
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OK -> B
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HH -> B
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OC -> P
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CV -> N
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SH -> O
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HK -> N
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NO -> F
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VF -> S
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NN -> O
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FK -> V
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HB -> O
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SS -> O
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FB -> B
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KS -> O
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CC -> S
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KF -> V
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VV -> S
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OP -> H
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KN -> F
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CS -> H
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CH -> P
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BF -> F
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NH -> O
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NK -> C
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OH -> C
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BH -> O
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FC -> V
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PB -> B
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18
aoc2021/input/day14_provided.txt
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18
aoc2021/input/day14_provided.txt
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@ -0,0 +1,18 @@
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NNCB
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CH -> B
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HH -> N
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CB -> H
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NH -> C
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HB -> C
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HC -> B
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HN -> C
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NN -> C
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BH -> H
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NC -> B
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NB -> B
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BN -> B
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BB -> N
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BC -> B
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CC -> N
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CN -> C
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160
aoc2021/src/day14.rs
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160
aoc2021/src/day14.rs
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@ -0,0 +1,160 @@
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use std::collections::{HashMap, HashSet, LinkedList};
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use std::fmt::Write;
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use anyhow::{Context, Result};
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const INPUT: &str = include_str!("../input/day14.txt");
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pub fn run() -> Result<String> {
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let mut res = String::with_capacity(128);
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writeln!(res, "part 1: {}", part1(INPUT)?)?;
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Ok(res)
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}
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fn part1(input: &str) -> Result<usize> {
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let (polymer, rules) = input.split_once("\n\n").context("couldn't split input")?;
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let mut polymer: Polymer = polymer.parse()?;
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let rules: Rules = rules.parse()?;
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let mut molecule_set = polymer.molecule_set();
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rules.0.values().for_each(|v| {
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molecule_set.insert(*v);
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});
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for _ in 0..10 {
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polymer.insert_pairs(&rules.0)?;
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}
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let occurrences = polymer.compute_occurrences(&molecule_set);
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let (_, least_common_occurrences) = occurrences
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.iter()
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.min_by_key(|(_, occurrences)| occurrences)
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.unwrap();
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let (_, most_common_occurrences) = occurrences
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.iter()
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.max_by_key(|(_, occurrences)| occurrences)
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.unwrap();
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Ok(most_common_occurrences - least_common_occurrences)
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}
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struct Rules(HashMap<(char, char), char>);
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impl std::str::FromStr for Rules {
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type Err = anyhow::Error;
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fn from_str(s: &str) -> Result<Self> {
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Ok(Self(
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s.lines()
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.map(str::trim)
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.map(|l| {
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let (pair, res) = l.split_once(" -> ").context("couldn't parse rule")?;
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Ok((
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(
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pair.chars().next().context("")?,
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pair.chars().nth(1).context("")?,
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),
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res.chars().next().context("couldn't parse rule")?,
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))
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})
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.collect::<Result<_>>()?,
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))
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}
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}
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#[derive(Debug)]
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struct Polymer {
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molecules: Option<LinkedList<char>>,
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}
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impl Polymer {
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fn insert_pairs(&mut self, rules: &HashMap<(char, char), char>) -> Result<()> {
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debug_assert!(self.molecules.is_some());
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self.molecules = Some(insert_pairs(
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std::mem::replace(&mut self.molecules, None).unwrap(),
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rules,
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)?);
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Ok(())
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}
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fn compute_occurrences(&self, molecule_set: &HashSet<char>) -> Vec<(char, usize)> {
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debug_assert!(self.molecules.is_some());
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let mut res = Vec::new();
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for molecule in molecule_set {
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let count = self
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.molecules
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.as_ref()
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.unwrap() // we always have a Some, Option only used for std::mem::replace
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.iter()
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.filter(|&m| m == molecule)
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.count();
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res.push((*molecule, count));
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}
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res
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}
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fn molecule_set(&self) -> HashSet<char> {
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debug_assert!(self.molecules.is_some());
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self.molecules.as_ref().unwrap().iter().copied().collect()
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}
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}
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impl std::str::FromStr for Polymer {
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type Err = anyhow::Error;
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fn from_str(s: &str) -> Result<Self> {
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let molecules = s.trim().chars().collect();
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Ok(Polymer {
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molecules: Some(molecules),
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})
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}
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}
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fn insert_pairs(
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mut molecules: LinkedList<char>,
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rules: &HashMap<(char, char), char>,
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) -> Result<LinkedList<char>> {
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if molecules.len() <= 1 {
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return Ok(molecules);
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}
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// List length is at least 2
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let mut iter = molecules.iter();
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let (left, right) = (*iter.next().unwrap(), *iter.next().unwrap());
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let to_insert = *rules
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.get(&(left, right))
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.with_context(|| format!("couldn't find rule for pair ({}, {})", left, right))?;
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let mut tail = insert_pairs(molecules.split_off(1), rules)?;
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molecules.push_back(to_insert);
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molecules.append(&mut tail);
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Ok(molecules)
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}
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#[cfg(test)]
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mod tests {
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use super::*;
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const PROVIDED: &str = include_str!("../input/day14_provided.txt");
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#[test]
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fn part1_provided() {
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assert_eq!(part1(PROVIDED).unwrap(), 1588);
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}
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#[test]
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fn part1_real() {
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assert_eq!(part1(INPUT).unwrap(), 3247);
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}
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}
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@ -13,3 +13,4 @@ pub mod day10;
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pub mod day11;
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pub mod day12;
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pub mod day13;
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pub mod day14;
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@ -15,6 +15,7 @@ use aoc2021::day10;
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use aoc2021::day11;
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use aoc2021::day12;
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use aoc2021::day13;
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use aoc2021::day14;
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fn main() -> Result<()> {
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let days: &[DayFunc] = &[
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day11::run,
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day12::run,
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day13::run,
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day14::run,
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];
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aoc::run(days)
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