void correctBST( Node root )

    {

        // Initialize pointers needed

        // for correctBSTUtil()

        first = middle = last = prev = null;

        // Set the pointers to find out

        // two nodes

        correctBSTUtil( root );

        // Fix (or correct) the tree

        if( first != null && last != null )

        {

            int temp = first.data;

            first.data = last.data;

            last.data = temp;

        }

        // Adjacent nodes swapped

        else if( first != null && middle !=

                                    null )

        {

            int temp = first.data;

            first.data = middle.data;

            middle.data = temp;

        }

        // else nodes have not been swapped,

        // passed tree is really BST.

    }