public int insert(int theKey, BinTreeNode root) {
        // insert an element with the specified key
        // overwrite old element if there is already an
        // element with the given key
        // return old element (if any) with key theKey
        // code to be completed
        BinTreeNode p = root, // set p as a pointer
                    pp = null;// set pp as the parent of p
        while(p!=null) {
            pp = p;// move pp to the child
            // move p to the child
            if(p.element > theKey)
                p = p.left;
            else if(p.element < theKey)
                p = p.right;
            else {// overwrite old element
                int returnKey = p.element;
                p.element = theKey;
                return returnKey;
            }
        }
        BinTreeNode r = new BinTreeNode(theKey);// create a new node for insert
        if(root != null)// check if the tree is not null
            if(pp.element > theKey)// determine where to insert
                pp.left = r;
            else
                pp.right = r;
        else
            root = r;
        return r.element;// return the inserted element