Need helping printing a recursion

Question

BST(T[] array) {
    constructBalancedTree(array, 0, array.length - 1);

}
void constructBalancedTree(T[] array, int i, int j) {
    if(i > j) {
        return;
    }

    int mid = (i+j)/2;
    Node node = new Node(array[mid]);

    constructBalancedTree(array, i, mid-1);
    constructBalancedTree(array, mid+1, j);
}

I'm trying to figure out how to print this out in the main. I have created:

BST<Integer> t1 = new BST<Integer>(new Integer[] {1, 5, 9, 12, 13, 15})

but when i try to print it out, it gives me a reference

Whats a Node here is also not defined. And where are you trying to save the result? — Naman, Nov 17 '16 at 04:21
that is what I have in my main and I cannot print out "System.out.println(t1);" it just gives me a reference error. — Robert Miller, Nov 17 '16 at 04:24
it's the default behavior of Object, override `toString()` in your class. — Jerry Chin, Nov 17 '16 at 04:26
@JerryChin Still don't understand how to print it in the main.. — Robert Miller, Nov 17 '16 at 04:31
@keving your code and explanation of your situation is obscure, all I can is to give you an advice, take a look at [how-to-use-the-tostring-method-in-java](http://stackoverflow.com/questions/3615721/how-to-use-the-tostring-method-in-java). — Jerry Chin, Nov 17 '16 at 04:45
**Please read** [How do I ask a good question?](http://stackoverflow.com/help/how-to-ask) before attempting to ask more questions. — , Jun 09 '17 at 15:21

score -1 · Answer 1 · answered Nov 17 '16 at 04:19

-1

You need to iterate through the array to print the elements in it. In Java an Array is an object so System.out.println(t1); in your case will print the reference to the object. Try

for(int i = 0; i < t1.length(); i++) {
    System.out.println(t1[i]);
 }

answered Nov 17 '16 at 04:19

minaco77

1
1
3

You shouldn't have to use a for loop in the main. – Robert Miller Nov 17 '16 at 04:20
I think OP means printing the tree after it has been constructed from the array. – sprinter Nov 17 '16 at 04:23
Yes. Here is my full code if it helps: http://pastebin.com/9SYJ584f – Robert Miller Nov 17 '16 at 04:24
@keving This loop is just for printing out the array values after you have returned the array from your method. – minaco77 Nov 17 '16 at 06:04

score -1 · Answer 2 · answered Nov 17 '16 at 05:11

I don't really understand what your code is supposed to do. It doesn't seem to be storing the node anywhere. I would expect that constructBalancedTree should be returning a node shouldn't it? Something like:

class BST {
    private Node root;

    BST(T[] array)  {
        root = constructBalancedTree(array, 0, array.length - 1);
    }

    private Node constructBalancedTree(T[] array, int i, int j) {
        if(i > j) {
            return null;
        } else {
            int mid = (i+j)/2;
            Node node = new Node(array[mid]);
            node.setLeft(constructBalancedTree(array, i, mid-1));
            node.setRight(constructBalancedTree(array, mid+1, j));
            return node;
        }
    }
}

In terms of printing the tree you have lots of options. You could add a toString method that recursive prints child nodes; you could use a Visitor design pattern to visit all nodes; you could have a method that gets the values as a list or stream:

class Node<T> {
    private Node left;
    private Node right;
    private T value;

    public Stream<T> getValues() {
        Stream.Builder<T> values = Stream.builder();
        if (left != null)
            left.getValues().forEach(values::accept);
        values.accept(value);
        if (right != null)
            right.getValues().forEach(values::accept);
        return values.build;
    }
}

Then you can just print the values: System.out.println(root.getValues().collect(Collectors.joining(", ")).

Need helping printing a recursion

2 Answers2