Question

Hi
I have an array list which has some numbers in it like {23,16,45,26,2,5,9}
and I want to make a binary search tree with this array list which is "array" and its elements are objects that has 2 fields,1)digit2)level but here I just want to use its digit field.Also dList is a DoublyLinkedList.
this is my code but it will throw an exception.please help me , thanks.

    private void method(ArrayList<Element> array) {
    DNode header = new DNode(null, null, null);
    DNode trailer = new DNode(null, header, null);
    header.next = trailer;
    DNode node = new DNode(array.get(0), header, trailer);
    dList.addLast(node);
    header = node
    for(int i = 1;i<array.size();i++){
    makeBST(node, array.get(i));
    }
}

private void makeBST(DNode node, Element e) {

    if (!e.equals(node.getElement())) {
        DNode nodeOne = new DNode(e, null, null);
        if (node.getElement().getDigit() > e.getDigit()) {
            node.prev = nodeOne;
        } else if (node.getElement().getDigit() < e.getDigit()) {
            node.next = node;
        }
    }
    if (e.getDigit() < node.getElement().getDigit()) {
        makeBST(node.prev, e);
    }
    makeBST(node.next, e);
}

Exception:

Exception in thread "main" java.lang.StackOverflowError
    at OBST.GreedyVersion.makeBST(GreedyVersion.java:43)
    at OBST.GreedyVersion.makeBST(GreedyVersion.java:54)
    at OBST.GreedyVersion.makeBST(GreedyVersion.java:54)
    at OBST.GreedyVersion.makeBST(GreedyVersion.java:54)

the first line of exception is for this line of code:

if (!e.equals(node.getElement())) 

Answer 1

your recursive method “private void makeBST(DNode node, Element e)” needs some type of ending condition (a flow path which will prevent it from calling itself); as it is, it keeps calling itself recursively which is what is causing your stack overflow error.