Interview Question for Computer Science Intern at Amazon.com:

The follow code could do the trick ...

int DupCount( Node *root )
{
    int count = 0;
    DoDupCount(root, count);
    Return count;
}
void DoDupCount(Node *root, int &count)
{
    if (root == NULL )
        return;

    // traversal , go left first
    DoDupCount(root->left, count);

    Bool flag = false;
    // traversal, go right until met different node
    While(root->right != NULL && root->right->data == root->data )
    {
        flag = true;
        root= root->right;
    }

    if (flag)
        count++;

    DoDupCount(root->right, count);
}