二进制搜索树更改插入方法返回类型

Question

I wrote an insert method for a binary search tree that is void . I have to change that method so that it returns a boolean but I am confused because my helper method for insert returns a Node .

Is there a way to write some other helper method that will return a boolean ? If not, how would I go about changing my method to return a boolean ?

This is my method:

public void insert(E s) 
{
    root = insert(s, root);
    root.setParent(findParent(root.getData()));
} 

private Node<E> insert(E s, Node<E> T)
{
    //easiest case, empty tree, create new tree
    if(T == null)
    {
        T = new Node<E>(s);
    }
    //s is greater than T, insert on right subtree
    else if(s.compareTo(T.getData()) > 0)
    {
        T.setRight(insert(s, T.getRight()));
    }
    //s is less than T, insert on left subtree
    else if (s.compareTo(T.getData()) < 0)
    {
        T.setLeft(insert(s,T.getLeft()));
    }
    else
    {
        System.out.println("Item already present.");

    }
    return T;
}//Close insert

Answer 1

I'm assuming you're supposed to return true if the insert is successful and false otherwise? Change your first insert function to look like this:

public boolean insert(E s) 
{
    try {
        root = insert(s, root);
        root.setParent(findParent(root.getData()));
        return true;
    } catch (Exception e) {
        return false;
    }
}

And change your helper function so that if the item is already present, it throws an Exception (for the main insert function to catch and trigger the false return).

private Node<E> insert(E s, Node<E> T) throws Exception {
    ...
    else {
        System.out.println("Item already present.");
        throw new Exception("Item already present.");
    }
    return T;
}

Or (as Tutankhamen suggests) return null from the helper method in the case of an unsuccessful insertion, so you have:

public boolean insert(E s) 
{
    root = insert(s, root);
    if (root == null) {
        return false;
    }
    root.setParent(findParent(root.getData()));
    return true;
}

private Node<E> insert(E s, Node<E> T) {
    ...
    else {
        System.out.println("Item already present.");
        return null;
    }
    return T;
}