Binary Search Tree Balancing

Question

I had a quesiton here, but it didn't save. I'm having trouble balancing a fully unbalanced tree (nodes 1-15 along the right side).

I'm having trouble because I get stack overflow.

> // balancing
    public void balance(node n) {
        if(n != null) {
            System.out.println(height(n)-levels);
            if (height(n.RCN) != height(n.LCN)) {
                if (height(n.RCN) > height(n.LCN)) {
                    if(height(n.RCN) > height(n.LCN)) {
                        n = rotateL(n);
                        n = rotateR(n);
                    } else {
                        n = rotateL(n);
                    }
                } else {
                    if(height(n.LCN) > height(n.RCN)) {
                        n = rotateR(n);
                        n = rotateL(n);
                    } else {
                        n = rotateR(n);
                    }
                }
                balance(n.LCN);
                balance(n.RCN);
            }
        }
    }

    // depth from node to left
    public int heightL(node n) {
        if (n == null)
            return 0;
        return height(n.LCN) + 1;
    }

    // depth from node from the right
    public int heightR(node n) {
        if (n == null)
            return 0;
        return height(n.RCN) + 1;
    }

    // left rotation around node
    public node rotateL(node n) {
        if (n == null)
            return null;
        else {
            node newRoot = n.RCN;
            n.RCN = newRoot.LCN;
            newRoot.LCN = n;
            return newRoot;
        }
    }

    // right rotation around node
    public node rotateR(node n) {
        if (n == null)
            return null;
        else {
            node newRoot = n.LCN;
            n.LCN = newRoot.RCN;
            newRoot.RCN = n;
            return newRoot;
        }
    }

Answer 1

Doing a rotateL followed by a rotateR ends up doing nothing since you are modifying the same node. n is not the original n. It is the newNode from the function. So basically, n is something like this:

newNode = rotateL(n);
n = rotateR(newNode);

So you are basically leaving the tree unchanged.

I am also unsure as to why you repeat the if (height(n.RCN) > height(n.LCN)) check. I think you meant your first check to be more like abs(height(n.RCN) - height(n.LCN)) > 1 and then use the comparison to determine which way to rotate.

Also, could you add the implementation for height(...)?