class Solution{
    public static int[] largestBSTBT(Node root)
    {
        if (root == null)
            return new int[] { Integer.MAX_VALUE,
                               Integer.MIN_VALUE, 0 };
        if (root.left == null && root.right == null)
            return new int[] { root.data, root.data, 1 };


        int[] left = largestBSTBT(root.left);
        int[] right = largestBSTBT(root.right);


        int[] ans = new int[3];


        if ((left[1] < root.data)
            && (right[0] > root.data)) {
            ans[0] = Math.min(left[0], Math.min(right[0], root.data));
            ans[1] = Math.max(right[1], Math.max(left[1], root.data));
            ans[2] = 1 + left[2] + right[2];
            return ans;
        }
        ans[0] = Integer.MIN_VALUE;
        ans[1] = Integer.MAX_VALUE;
        ans[2] = Math.max(left[2], right[2]);

        return ans;
    }

    public static int largestBSTBTutil(Node root)
    {

        return largestBSTBT(root)[2];
    }
}