Function pred

src/tree/binary/bst.rs:175–199

# Safety This is highly unsafe, due to pointer

(
    node: Option<NonNull<Node<K, V>>>,
    mut key: &'a K,
)

///
/// This is highly unsafe, due to pointer
unsafe fn pred<'a, K: 'a, V: 'a>(
    node: Option<NonNull<Node<K, V>>>,
    mut key: &'a K,
) -> Option<NonNull<Node<K, V>>>
where
    K: Ord,
{
    find(node, key).and_then(|node| {
        let mut nq = NodeQuery::new(Some(node));
        match nq.left().node {
            //左分支的最大值
            Some(l) => find_max(Some(l)),
            None => {
                //左分支为空，向上找
                loop {
                    nq = nq.parent();
                    match nq.left_key() {
                        Some(l) if l == key => key = nq.get_key().unwrap(),
                        _ => return nq.node,
                    }
                }
            }
        }
    })
}

/// # Safety
///