Adding objects to binary search tree

Question

I'm completely new to BST and how they work if this is completely wrong it would be appreciated if I could get a link to a reference site or something. right now I'm writing a program to add values from an ArrayList of Strings to a BST and I come up with errors such as The method compareTo(Node) is undefined for the type ArrayList<String>. I thought by having extends Comparable it would account for comparing ArrayList values but I'm not using E. Also I had to add a cast to s to set it as the root but I feel like there is an easier way. I don't know if I can add ArrayList values the way I'm doing it, this is just how it looks in the book I'm using for reference. This is my code, any help would be appreciated, I already tried looking up things in the Java API and that didn't help:

public class BinarySearchTree<E extends Comparable<? super E>>

{

    public void add(ArrayList<String> s, Node n) {


            if (n == null)
                 n = (Node) s;
            else if (s.compareTo(n) < 0)
                 add(s, n.leftChild);
            else
                 add(s, n.rightChild);


    }
}

what exactly does "add()" do? it seems like you're trying to add ArrayLists into a BST, rather than add values FROM and ArrayList into the BST — mfsiega
– mfsiega, Commented Mar 18, 2012 at 18:25

user1270627 · Accepted Answer · 2012-03-18 19:11:24Z

1

I think this reference would be helpful to you: Binary Search Trees - Stanford Library

answered Mar 18, 2012 at 19:11

user1270627

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1 Comment

SeattleOrBayArea Over a year ago

This is one of the best references I have seen.

Noroi · Accepted Answer · 2012-03-18 18:38:47Z

1

First of all, the Node class should extend Comparable and override the compareTo method in it. ArrayList class doesn't extend Comparable and hence the following will not work

s.compareTo(n) < 0

s being an ArrayList reference. Also, you are trying to compare an ArrayList reference with a Node reference which is totally incorrect. You need to compare two Node values.

answered Mar 18, 2012 at 18:38

Noroi

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Comments

Ted Hopp · Accepted Answer · 2012-03-18 18:35:53Z

0

It looks like you are trying to add the entire ArrayList as a single node of your BST. My guess is that you are supposed to construct a BST from the elements of the ArrayList. For that, I would suggest defining two functions:

public Node add(ArrayList<String> s, Node root) {
    for (String elt : s) {
        root = add(elt, root);
    }
}

public Node add(String elt, Node root) {
    if (root == null) {
        root = // new Node with data set to elt
    } else if (elt.compareTo(n.data()) < 0) {
        root.left = add(elt, root.left);
    } else if (elt.compareTo(n.data()) > 0) {
        root.right = add(elt, root.right);
    } else {
        // duplicate element being inserted -- error?
    }
    return root;
}

answered Mar 18, 2012 at 18:35

Ted Hopp

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1 Comment

Ryan Sayles Over a year ago

Yes I do have to add each element from the ArrayList to a BST. Thank you for the help! One question though, what do you mean by n.data(). Should I set n to each value in the ArrayList?

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