Function postorder

publication/code/chapter08/binary_tree.rs:306–312

(bt: Link<T>)

}

fn postorder<T: Clone + Ord + ToString + Debug>(bt: Link<T>) {
    if !bt.is_none() {
        postorder(bt.as_ref().unwrap().get_left());
        postorder(bt.as_ref().unwrap().get_right());
        println!("key: {:?}", bt.as_ref().unwrap().get_key());
    }
}

fn levelorder<T: Clone + Ord + ToString + Debug>(bt: Link<T>) {
    if bt.is_none() { return; }