如何使用三个参数将节点插入到 Treap 上

Question

我在将 Treapnode 插入 Treap 时遇到问题。它接受 3 个参数。添加（E 键，P 优先级，treapnode x）。我尝试了很多方法，但总是出现空指针异常。我尝试检查左右树中的空情况。private TreapNode add (E key, P priority, TreapNode x)        throws ElementFoundException {    // For You To Complete    int compare = key.compareTo(x.element());    if (x == null){        return new TreapNode(key, priority);    }    //root is larger than the key    else if (compare == 0) {        throw new ElementFoundException("Element was found, and tree was not changed.");    } else if (compare < 0) {        if (x.left() == null) {         //TreapNode y = new TreapNode(key, priority);            TreapNode y = x.left;            x.left = y.right;            y.right = x;            return y;        } else {            x.left = add(key, priority, x.left());        }    }    //root is smaller than the key    else if (compare > 0) {        if (x.right() == null) {            //TreapNode y = new TreapNode(key, priority);            TreapNode z = x.right;            x.right = z.left;            z.left = x;            return z;        }    }    return x;}

Answer 1

这是你做错了x.right()。情况也是如此x.left()

if (x.right() == null) {

        //TreapNode y = new TreapNode(key, priority);

        TreapNode z = x.right; // z = null

        x.right = z.left;  // z.left will throw NPE

应该

if (x.right() == null) {

   x.right() = new TreapNode(key, priority);

   return x; // return parent node 

}

另外，我认为这也是一个错误的比较，int不能null但是Integer类可以

int compare = key.compareTo(x.element());  //comoareTo return an int 

if (x == null){  // does not make sense to compare and int type to Object type

  ....

}