Method none_leaf_size

publication/code/chapter08/binary_tree.rs:109–111

计算非叶节点数 [千万不要想复杂了]

(&self)

    // 计算非叶节点数 [千万不要想复杂了]
    fn none_leaf_size(&self) -> usize {
        self.size() - self.leaf_size()
    }

    // 计算树深度
    fn depth(&self) -> usize {