Day 14, part 2
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src/day14.rs
83
src/day14.rs
@ -1,34 +1,33 @@
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use std::collections::HashMap;
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fn expand(depth: usize, left: char, right: char, rules: &[(char, char, char)], elements: &mut HashMap<char, usize>) {
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if depth == 0 {
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return;
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}
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match rules.iter().find(|rule| rule.0 == left && rule.1 == right) {
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Some(rule) => {
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let counter = elements.entry(rule.2).or_insert(0);
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*counter += 1;
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expand(depth - 1, left, rule.2, rules, elements);
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expand(depth - 1, rule.2, right, rules, elements);
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}
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None => {}
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}
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}
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fn polymerize(depth: usize, template: &str, rules: &[(char, char, char)]) -> (usize, usize) {
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let mut elements: HashMap<char, usize> = HashMap::new();
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let chars = &template.chars().collect::<Vec<char>>();
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let chars = template.chars().collect::<Vec<char>>();
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for pair in chars.windows(2) {
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let (left, right) = (pair[0], pair[1]);
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let counter = elements.entry(left).or_insert(0);
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*counter += 1;
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expand(depth, left, right, rules, &mut elements);
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let mut elements: HashMap<char, usize> = HashMap::new();
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for element in chars {
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*(elements.entry(*element).or_insert(0)) += 1;
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}
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// Add the last (right-side) element.
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let counter = elements.entry(*chars.last().unwrap()).or_insert(0);
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*counter += 1;
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let mut pairs: HashMap<(char, char), usize> = HashMap::new();
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for pair in chars.windows(2) {
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*(pairs.entry((pair[0], pair[1])).or_insert(0)) += 1;
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}
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for _ in 0..depth {
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let mut p = pairs.clone();
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for (pair, n) in pairs.iter() {
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if let Some(rule) = rules
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.iter()
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.find(|rule| rule.0 == pair.0 && rule.1 == pair.1)
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{
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*(p.entry((pair.0, rule.2)).or_insert(0)) += n;
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*(p.entry((rule.2, pair.1)).or_insert(0)) += n;
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*(p.entry((pair.0, pair.1)).or_insert(0)) -= n;
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*(elements.entry(rule.2).or_insert(0)) += n;
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}
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}
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pairs = p;
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}
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let least_common = elements.iter().min_by(|x, y| x.1.cmp(y.1)).unwrap().1;
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let most_common = elements.iter().max_by(|x, y| x.1.cmp(y.1)).unwrap().1;
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@ -38,22 +37,23 @@ fn polymerize(depth: usize, template: &str, rules: &[(char, char, char)]) -> (us
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fn main() {
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const INPUT: &str = include_str!("../inputs/day14.txt");
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let (template, rules) = INPUT.split_once("\n\n").unwrap();
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let (least_common, most_common) = polymerize(
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10,
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template,
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&rules
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.lines()
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.map(|rule| rule.split_once(" -> ").unwrap())
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.map(|(a, b)| {
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let mut pair = a.chars();
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(
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pair.next().unwrap(),
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pair.next().unwrap(),
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b.chars().next().unwrap(),
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)
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})
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.collect::<Vec<(char, char, char)>>(),
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);
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let rules = rules
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.lines()
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.map(|rule| rule.split_once(" -> ").unwrap())
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.map(|(a, b)| {
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let mut pair = a.chars();
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(
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pair.next().unwrap(),
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pair.next().unwrap(),
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b.chars().next().unwrap(),
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)
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})
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.collect::<Vec<(char, char, char)>>();
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let (least_common, most_common) = polymerize(10, template, &rules);
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println!("solution {}", most_common - least_common);
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let (least_common, most_common) = polymerize(40, template, &rules);
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println!("solution {}", most_common - least_common);
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}
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@ -79,4 +79,5 @@ fn test_polymerize() {
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('C', 'N', 'C'),
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];
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assert_eq!(polymerize(10, "NNCB", &rules), (161, 1749));
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assert_eq!(polymerize(40, "NNCB", &rules), (3849876073, 2192039569602));
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}
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