Tree minimum

The minimum pub API returns the minimum entry in the tree if the tree is not empty. It call anoth-ther internal API called min. The min function accepts a reference to Rc<RefCell<Node<T>>> and returns OptionRc<RefCell<Node<T>>>>. Its does so by going to the left of the passed in node reference as far as possible or returns current left's root node otherwise.

The tree minimum just calls the internal min function passing its root node's reference and returns either returned Node's (if found) key or None otherwise.

Below are the public minimum and internal min APIs.

    //Returns the minimum key value (if any) or `None` otherwise
    //Delegates to internal min function
    pub fn minimum(&self) -> Option<T> {
        let node = self.root();
        match node {
            None => None,
            Some(ref inner) => Self::min(inner).map(|n| n.borrow().key.clone()),
        }
    }

Note: This is one place where we are using clone on T i.e. key.clone() above.

    //Find the min - given a node. Result could be given node itself
    //if no more left branch is there
    fn min(node: &Rc<RefCell<Node<T>>>) -> Option<Rc<RefCell<Node<T>>>> {
        match node.borrow().left_node() {
            Some(ref left_node) => Self::min(left_node),
            None => Some(Rc::clone(node)),
        }
    }