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use std::collections::{HashMap, HashSet};
fn main() {
let input = advent::read_lines(19);
println!("19a: {}", distinct_molecules(&input));
println!("19b: {}", 0);
}
fn distinct_molecules(input: &[String]) -> usize {
let mut input = input.to_owned();
let molecule = input.pop().unwrap();
input.pop(); // drop empty line
let mut replacements = HashMap::new();
for line in input {
let replacement : Vec<_> = line.split(" => ").collect();
let (left, right) = (replacement[0].to_string(), replacement[1].to_string());
replacements.entry(left).or_insert(Vec::new()).push(right);
}
let mut result = HashSet::new();
for (left, rights) in replacements {
for right in rights {
for i in 0 .. molecule.len() {
let check_pos = std::cmp::min(i + left.len(), molecule.len());
if molecule[i..check_pos].contains(&left) {
let new_molecule = molecule[0..i].to_string()
+ &right
+ &molecule[(i + left.len())..];
result.insert(new_molecule);
}
}
}
}
result.len()
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn test() {
let mut input = Vec::from([
"H => HO".to_string(),
"H => OH".to_string(),
"O => HH".to_string(),
"".to_string(),
"HOH".to_string(),
]);
assert_eq!(distinct_molecules(&input), 4);
input.pop();
input.push("HOHOHO".to_string());
assert_eq!(distinct_molecules(&input), 7);
}
}
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