Question

I posted a question related to this topic earlier, but I’m having trouble figuring this out as well. I’m trying to search an unordered binary tree by a key value and return its associated value through a recursive function.

The class has the form:

  Class Node
  {
     private:
       Node *leftChild;
       Node *rightChild;
       int key;
       int value;
 }

With each variable having associated get methods. So I basically want to search through the binary tree and return its value once I get to the correct Node.

Here is my attempt thus far, I think I’m pretty close:

int preOrder(Node *node, int key)
{
   if(node->getKey() == key)
     return node->getValue();

  Node* leftNode = node->getLeft();

  if(leftNode != NULL)
  {
    return preOrder(leftNode, key);
  }

  Node* rightNode = node->getRight();

  if(rightNode != NULL)
  {
    return preOrder(rightNode, key);
  }

  //I know a return statement needs to be placed here
  //in case both pointers are NULL in order to return to the previous
  //node in the tree, but I'm not sure how to do this...
}

Does anyone have any advice?

Answer 1

Here you go. This includes the code to answer your last question, modified to support Key/Value nodes instead of just Value nodes. Also, with the changes it made sense to return a pointer to the node rather than the value it contained, so I updated lowest to do it that way as well.

template <typename KeyT, typename ValueT>
class Node
{
public:
    Node(KeyT k, ValueT v)
    {
        key = k;
        value = v;
        right = NULL;
        left = NULL;
    }

    Node<KeyT, ValueT> * lowest()
    {
        Node<KeyT, ValueT> * v = this;

        if (right != NULL)
            if (v->value > left->value) v = left;
        if (left  != NULL)
            if (v->value > right->value) v = right;

        return v;
    }

    Node<KeyT, ValueT> * searchByKey(KeyT k)
    {
        if (key == k)
            return this;

        Node<KeyT, ValueT> * n = NULL;

        if (left != NULL)
            n = left->searchByKey(k);
        if (n != NULL) return n;
        if (right!= NULL)
            n = right->searchByKey(k);
        if (n != NULL) return n;

        return NULL;
    }

    Node<KeyT, ValueT> * getRight()
    {
        return right;
    }

    Node<KeyT, ValueT> * getLeft()
    {
        return left;
    }

    void setRight(Node<KeyT, ValueT> * nright)
    {
        right = nright;
    }

    void setLeft(Node<KeyT, ValueT> * nleft)
    {
        left = nleft;
    }

    KeyT getKey()
    {
        return key;
    }

    ValueT getValue()
    {
        return value;
    }

private:
    KeyT   key;
    ValueT value;

    Node<KeyT, ValueT> * right;
    Node<KeyT, ValueT> * left;
};

Look at example output: http://ideone.com/l5ZNc