Calculate size of vertex cover when root is not part of it
int size_excl = 0 ; if ( root . left != null ) size_excl += 1 + vCover ( root . left . left ) + vCover ( root . left . right ) ; if ( root . right != null ) size_excl += 1 + vCover ( root . right . left ) + vCover ( root . right . right ) ;