use collections::*;

fn main() {
    let mut db = HashMap::new();
    db.insert("hash1", vec![1, 2, 3]);

    let mut state: HashSet<_, Vec<usize>> = HashMap::new();

    for hash in xxx {
    if let Some(entry) = db.get(hash) {
        state.entry(hash).or_default().extend_from_slice(&entry);
    }

    let a = BTreeMap::new()

    for hash in a.index("ha1".."ha5")
}