void insert(string key, Object o);
Object lookup(string key);
void remove(string key);

class BinarySearchTree
{
  struct TreeNode
  {
    string key;
    Object info;
    TreeNode * left, * right;
    TreeNode(string k, Object in, TreeNode * l, TreeNode * r)
    {
      key = k; info = in; left = l; right = r;
    }
    static TreeNode * find(string k, TreeNode * t);
    static TreeNode * insert(string k, Object in, TreeNode * t);
    static TreeNode * remove(string k, TreeNode * t);
    static void destruct(TreeNode * t);
  };
  TreeNode * root;
public:
  BinarySearchTree();
  void insert(string key, Object info);
  Object lookup(string key);
  void remove(string key);
  ~BinarySearchTree();
};

void preorder(TreeNode * root)
{
  if (root != null)
  {
    cout << root->info;
    preorder(root->left);
    preorder(root->right);
  }
}

void inorder(TreeNode * root)
{
  if (root != null)
  {
    inorder(root->left);
    cout << root->info;
    inorder(root->right);
  }
}

void postorder(TreeNode * root)
{
  if (root != null)
  {
    postorder(root->left);
    postorder(root->right);
    cout << root->info;
  }
}

// returns the last node to the right of node t
template
  <typename T>
void swap(T & A, T & B)
{
  T X = A;
  A = B;
  B = X;
}
void swapKeyAndInfo(TreeNode * t1, TreeNode * t2);
{
  swap(t1->key, t2->key);
  swap(t1->info, t2->info);
}
TreeNode * rightMost(TreeNode * t)
{
  while ( t->right )
    t = t->right;
  return t;
}
TreeNode * removeThisNode(TreeNode *t)
{   // of course, we must deal with deleting removed node
  if (!t->left)
    return t->right;
  else if (!t->right)
    return t->left;
  else // the hard case, it has two children
  {
    TreeNode * rightMostOfLeft = rightMost(t->left);
    swapKeyAndInfo(t, rightMostOfLeft);
    t->left = remove(key, t->left);
  }
}
BinarySearchTree::TreeNode *
  BinarySearchTree :: remove(string key, TreeNode * t)
{
  if (t == 0)
    return 0;
  if (key < t->key)
    t->left = remove(key, t->left);
  else if (key > t->key)
    t->right = remove(key, t->right);
  else
    t = removeThisNode(t);
  return t;
}