#[derive(PartialEq, Debug)]
pub enum Comparison {
    Equal,
    Unequal,
    Sublist,
    Superlist,
}

fn sublists<'a, T>(l: &'a [T]) -> impl 'a + Iterator {
    let empty: &[T] = &[]; // I can't put this directly in once as it gets seen as &[_; 0]
    std::iter::once(empty).chain((0..l.len()).flat_map(move |i| l.windows(i)))
}

pub fn sublist<T>(l1: &[T], l2: &[T]) -> Comparison
where
    T: PartialEq,
{
    if l1 == l2 {
        Comparison::Equal
    } else if sublists(l2).find(l1).is_some() {
        Comparison::Sublist
    } else if sublists(l1).find(l2).is_some() {
        Comparison::Superlist
    } else {
        Comparison::Unequal
    }
}

fn main() {
    assert_eq!(Comparison::Sublist, sublist(&[1, 2, 3], &[1, 2, 3, 4, 5]));
}