void Insert(Tree * p, int key, char direction)
// precondition: P is not NULL/0.  If direction is 'R',
//               P has a right child; if direction is 'L',
//               P has a left child.
// postcondition: If direction is 'R', a node containing the    
//                value key is created and inserted between P and
//                P's right child.
//                If direction is 'L', a node containing the    
//                value key is created and inserted between P and
//                P's left child.
{
    if (p != NULL)   // be safe even with precondition
    {
	if (direction == 'R')
	{
	    p->right = new Tree(key, NULL, p->right);
	}
	else if (direction == 'L')
	{
	    p->left = new Tree(key,p->left);
	}
    }
}