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Day 14, part 2

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Zoé Cassiopée Gauthier 2021-12-14 11:59:23 -05:00
parent daaa7f9fb4
commit 2c1f191fe1
1 changed files with 42 additions and 41 deletions
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63
src/day14.rs
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@ -1,34 +1,33 @@
use std::collections::HashMap; use std::collections::HashMap;
fn expand(depth: usize, left: char, right: char, rules: &[(char, char, char)], elements: &mut HashMap<char, usize>) {
if depth == 0 {
return;
}
match rules.iter().find(|rule| rule.0 == left && rule.1 == right) {
Some(rule) => {
let counter = elements.entry(rule.2).or_insert(0);
*counter += 1;
expand(depth - 1, left, rule.2, rules, elements);
expand(depth - 1, rule.2, right, rules, elements);
}
None => {}
}
}
fn polymerize(depth: usize, template: &str, rules: &[(char, char, char)]) -> (usize, usize) { fn polymerize(depth: usize, template: &str, rules: &[(char, char, char)]) -> (usize, usize) {
let mut elements: HashMap<char, usize> = HashMap::new(); let chars = &template.chars().collect::<Vec<char>>();
let chars = template.chars().collect::<Vec<char>>(); let mut elements: HashMap<char, usize> = HashMap::new();
for pair in chars.windows(2) { for element in chars {
let (left, right) = (pair[0], pair[1]); *(elements.entry(*element).or_insert(0)) += 1;
let counter = elements.entry(left).or_insert(0);
*counter += 1;
expand(depth, left, right, rules, &mut elements);
} }
// Add the last (right-side) element. let mut pairs: HashMap<(char, char), usize> = HashMap::new();
let counter = elements.entry(*chars.last().unwrap()).or_insert(0); for pair in chars.windows(2) {
*counter += 1; *(pairs.entry((pair[0], pair[1])).or_insert(0)) += 1;
}
for _ in 0..depth {
let mut p = pairs.clone();
for (pair, n) in pairs.iter() {
if let Some(rule) = rules
.iter()
.find(|rule| rule.0 == pair.0 && rule.1 == pair.1)
{
*(p.entry((pair.0, rule.2)).or_insert(0)) += n;
*(p.entry((rule.2, pair.1)).or_insert(0)) += n;
*(p.entry((pair.0, pair.1)).or_insert(0)) -= n;
*(elements.entry(rule.2).or_insert(0)) += n;
}
}
pairs = p;
}
let least_common = elements.iter().min_by(|x, y| x.1.cmp(y.1)).unwrap().1; let least_common = elements.iter().min_by(|x, y| x.1.cmp(y.1)).unwrap().1;
let most_common = elements.iter().max_by(|x, y| x.1.cmp(y.1)).unwrap().1; let most_common = elements.iter().max_by(|x, y| x.1.cmp(y.1)).unwrap().1;
@ -38,10 +37,7 @@ fn polymerize(depth: usize, template: &str, rules: &[(char, char, char)]) -> (us
fn main() { fn main() {
const INPUT: &str = include_str!("../inputs/day14.txt"); const INPUT: &str = include_str!("../inputs/day14.txt");
let (template, rules) = INPUT.split_once("\n\n").unwrap(); let (template, rules) = INPUT.split_once("\n\n").unwrap();
let (least_common, most_common) = polymerize( let rules = rules
10,
template,
&rules
.lines() .lines()
.map(|rule| rule.split_once(" -> ").unwrap()) .map(|rule| rule.split_once(" -> ").unwrap())
.map(|(a, b)| { .map(|(a, b)| {
@ -52,8 +48,12 @@ fn main() {
b.chars().next().unwrap(), b.chars().next().unwrap(),
) )
}) })
.collect::<Vec<(char, char, char)>>(), .collect::<Vec<(char, char, char)>>();
);
let (least_common, most_common) = polymerize(10, template, &rules);
println!("solution {}", most_common - least_common);
let (least_common, most_common) = polymerize(40, template, &rules);
println!("solution {}", most_common - least_common); println!("solution {}", most_common - least_common);
} }
@ -79,4 +79,5 @@ fn test_polymerize() {
('C', 'N', 'C'), ('C', 'N', 'C'),
]; ];
assert_eq!(polymerize(10, "NNCB", &rules), (161, 1749)); assert_eq!(polymerize(10, "NNCB", &rules), (161, 1749));
assert_eq!(polymerize(40, "NNCB", &rules), (3849876073, 2192039569602));
} }