sol.rs

let mut head = Node::new(vec[0].clone());
let mut current_head: &mut Node<T> = &mut head;

for &next in &vec[1..] {
    let moved_head = current_head; // Takes the mutable reference away from current_head
    moved_head.right = Some(Box::new(Node::new(next.clone())));
    current_head = moved_head.right.as_mut().unwrap();
}