How to insert element in binary tree by recursion?

问题

void Btree<T>::InsertNode2(T data, BtreeNode* root)
{
    if (root==NULL)
    {
        root = new BtreeNode (data);
        return ;
    }
    if (data <= root->data)
        InsertNode2(data, root->leftchild);
    else
        InsertNode2(data, root->rightchild);
}

Why isn't it right? The root can't be assigned correctly. After calling the function it's still NULL.

回答1:

It almost correct. Just, as said by @DragonMoon, all you need to do is to pass root by reference

void Btree<T>::InsertNode2(T data, BtreeNode &* root)
{
    if (root==NULL)
    {
        root = new BtreeNode (data);
        return ;
    }
    if (data <= root->data)
        InsertNode2(data, root->leftchild);
    else
        InsertNode2(data, root->rightchild);
}

来源：https://stackoverflow.com/questions/43373161/how-to-insert-element-in-binary-tree-by-recursion