gistfile1.rs

#[deriving(Clone)]
struct CountedSet<T> {
    data: HashMap<T, uint>
}

fn subtract(&self, other: &CountedSet<T>) -> CountedSet<T> {
    let mut result = self.clone();
    for (key, count) in other.iter() {
        match result.data.find_copy(key) {
            Some(old) => {
               let difference = if old > *count {old - *count} else { 0 };
               result.data.insert((*key).clone(), difference);
            }
            _ => {}
        }
    }
    result
}