Rust
Technically you don't need to store the names in part 3, but I was too lazy.
use std::collections::{HashMap, HashSet};
pub fn solve_part_1(input: &str) -> String {
let (names, rules) = input.split_once("\n\n").unwrap();
let names: Vec<&str> = names.split(",").collect();
let rules: HashMap<char, HashSet<char>> = rules
.lines()
.map(|line| {
let (from, to) = line.split_once(" > ").unwrap();
let to = to.split(",");
(
from.chars().next().unwrap(),
to.map(|s| s.chars().next().unwrap()).collect(),
)
})
.collect();
for name in names {
let mut allowed_chars = rules.get(&name.chars().next().unwrap());
let mut acceptable = true;
for ch in name.chars().skip(1) {
match allowed_chars {
Some(allowed) => {
if !allowed.contains(&ch) {
acceptable = false;
break;
}
allowed_chars = rules.get(&ch);
}
None => {
panic!("no rules for letter {ch} in name {name}");
}
}
}
if acceptable {
return name.to_string();
}
}
panic!("all names bad");
}
pub fn solve_part_2(input: &str) -> String {
let (names, rules) = input.split_once("\n\n").unwrap();
let names: Vec<&str> = names.split(",").collect();
let rules: HashMap<char, HashSet<char>> = rules
.lines()
.map(|line| {
let (from, to) = line.split_once(" > ").unwrap();
let to = to.split(",");
(
from.chars().next().unwrap(),
to.map(|s| s.chars().next().unwrap()).collect(),
)
})
.collect();
let mut sum_of_indices = 0;
for (i, name) in names.into_iter().enumerate() {
let mut allowed_chars = rules.get(&name.chars().next().unwrap());
let mut acceptable = true;
for ch in name.chars().skip(1) {
match allowed_chars {
Some(allowed) => {
if !allowed.contains(&ch) {
acceptable = false;
break;
}
allowed_chars = rules.get(&ch);
}
None => {
panic!("no rules for letter {ch} in name {name}");
}
}
}
if acceptable {
sum_of_indices += 1 + i;
}
}
sum_of_indices.to_string()
}
fn gen_names_with_prefix(
prefix: &str,
rules: &HashMap<char, HashSet<char>>,
result: &mut HashSet<String>,
) {
if prefix.len() >= 7 {
result.insert(prefix.to_string());
}
if prefix.len() == 11 {
return;
}
let last_char = prefix.chars().last().unwrap();
if let Some(next_chars) = rules.get(&last_char) {
for next_char in next_chars {
let new_prefix = format!("{prefix}{next_char}");
gen_names_with_prefix(new_prefix.as_str(), rules, result);
}
}
}
pub fn solve_part_3(input: &str) -> String {
let (prefix, rules) = input.split_once("\n\n").unwrap();
let prefixes: Vec<_> = prefix.split(",").collect();
let rules: HashMap<char, HashSet<char>> = rules
.lines()
.map(|line| {
let (from, to) = line.split_once(" > ").unwrap();
let to = to.split(",");
(
from.chars().next().unwrap(),
to.map(|s| s.chars().next().unwrap()).collect(),
)
})
.collect();
let mut results: HashSet<String> = HashSet::new();
prefixes
.into_iter()
.filter(|&name| {
let mut allowed_chars = rules.get(&name.chars().next().unwrap());
let mut acceptable = true;
for ch in name.chars().skip(1) {
match allowed_chars {
Some(allowed) => {
if !allowed.contains(&ch) {
acceptable = false;
break;
}
allowed_chars = rules.get(&ch);
}
None => {
panic!("no rules for letter {ch} in name {name}");
}
}
}
acceptable
})
.for_each(|prefix| gen_names_with_prefix(prefix, &rules, &mut results));
results.len().to_string()
}