Function rotate_left

src/tree/binary/rb2.rs:305–313

h x / \ / \ A R(x) => R(h) C / \ / \ B C A B 旋转操作会改变红链接的指向，所以旋转之后 h 变为 R(h) 旋转操作可以保持rb tree的两个重要性质：有序性(中序)和完美平衡性 */ make a right-leaning link lean to the left

(h: Option<NonNull<Node<K, V>>>)

*/
/// make a right-leaning link lean to the left
fn rotate_left<K, V>(h: Option<NonNull<Node<K, V>>>) -> Option<NonNull<Node<K, V>>> {
    let mut h = NodeQuery::new(h);
    let mut x = h.right();
    h.set_right(x.left().node);
    x.set_left(h.node);
    x.set_color(h.color().unwrap());
    h.set_color(Color::Red);
    x.node
}

/*
       h                x