largest bst in binary tree

class bst
{ public:
    int min;
    int max;
    int size;
    
    bst(int max,int min,int size)
    {
        this->min=min;
        this->max=max;
        this->size=size;
    }
};
bst checkforbst(TreeNode<int>*root)
{
    if(root==NULL)
        return bst(INT_MIN,INT_MAX,0);
    auto l=checkforbst(root->left);
    auto r=checkforbst(root->right);
    if(l.max < root->data && root->data < r.min)
    {
        return bst(max(root->data,r.max),min(root->data , l.min),(l.size+r.size)+1);
    }
    return bst(INT_MAX,INT_MIN,max(l.size,r.size));
}
int largestBST(TreeNode<int>* root) 
{
    return checkforbst(root).size;
}