Use std::cmp::Ordering; use std::collections::BTreeMap; pub fn merge_union<K, A, B>(left: BTreeMap<K, A>, right:

Question

Use std::cmp::Ordering; use std::collections::BTreeMap; pub fn merge_union<K, A, B>(left: BTreeMap<K, A>, right:

BTreeMap<K, B>) -> BTreeMap<K, (A, B)>
where
K: Ord,
{
let mut result = vec![];
let (mut left, mut right) = (left.into_iter(), right.into_iter());
let (mut pl, mut pr) = (left.next(), right.next());

while pl.is_some() && pr.is_some() {
let (l, r) = pl.as_ref().zip(pr.as_ref()).unwrap();
match l.0.cmp(&r.0) {
Ordering::Less => pl = left.next(),
Ordering::Greater => pr = right.next(),
Ordering::Equal => {
let ((k, a), (_, b)) = pl.zip(pr).unwrap();
result.push((k, (a, b)));
(pl, pr) = (left.next(), right.next());
}
}
}

result.into_iter().collect()
}

fn main() {
let a = BTreeMap::from_iter([(1, "a"), (3, "c"), (4, "d"), (5, "e")]);
let b = BTreeMap::from_iter([(2, 2), (3, 3), (5, 5), (7, 7)]);
let ab = merge_union(a, b);
println!("{ab:?}");
}