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use advent_of_code::prelude::*;
fn small(s: &str) -> bool {
s.bytes().all(|c| c.is_ascii_lowercase())
}
fn single_small<'a>(path: impl Iterator<Item = &'a str>) -> bool {
let mut set = HashSet::new();
for s in path {
if !small(s) {
continue;
}
if set.contains(s) {
return false;
}
set.insert(s);
}
true
}
fn paths_from1<'a>(
graph: &'a HashMap<String, HashSet<String>>,
path: &mut Vec<&'a str>,
) -> u64 {
let mut total = 0;
for neighbor in graph[path[path.len() - 1]].iter() {
if small(neighbor) && path.contains(&neighbor.as_ref()) {
continue;
}
if neighbor == "end" {
total += 1;
} else {
path.push(neighbor);
total += paths_from1(graph, path);
path.pop();
}
}
total
}
fn paths_from2<'a>(
graph: &'a HashMap<String, HashSet<String>>,
path: &mut Vec<&'a str>,
) -> u64 {
let mut total = 0;
for neighbor in graph[path[path.len() - 1]].iter() {
if neighbor == "start" {
continue;
}
if small(neighbor)
&& path.contains(&neighbor.as_ref())
&& !single_small(path.iter().copied())
{
continue;
}
if neighbor == "end" {
total += 1;
} else {
path.push(neighbor);
total += paths_from2(graph, path);
path.pop();
}
}
total
}
pub fn parse(fh: File) -> Result<HashMap<String, HashSet<String>>> {
let mut graph = HashMap::new();
for line in parse::raw_lines(fh) {
let nodes: Vec<_> = line.split('-').map(|s| s.to_string()).collect();
let edges =
graph.entry(nodes[0].clone()).or_insert_with(HashSet::new);
edges.insert(nodes[1].clone());
let edges =
graph.entry(nodes[1].clone()).or_insert_with(HashSet::new);
edges.insert(nodes[0].clone());
}
Ok(graph)
}
pub fn part1(graph: HashMap<String, HashSet<String>>) -> Result<u64> {
Ok(paths_from1(&graph, &mut vec!["start"]))
}
pub fn part2(graph: HashMap<String, HashSet<String>>) -> Result<u64> {
Ok(paths_from2(&graph, &mut vec!["start"]))
}
#[test]
fn test() {
assert_eq!(
part1(parse(parse::data(2021, 12).unwrap()).unwrap()).unwrap(),
3230
);
assert_eq!(
part2(parse(parse::data(2021, 12).unwrap()).unwrap()).unwrap(),
83475
);
}
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