304 // Problems with mutability and parallel computations

   305 //====================================================

   306 

   307 def count_intersection(A: Set[Int], B: Set[Int]) : Int = {

   308   var count = 0

   309   for (x <- A; if (B contains x)) count += 1 

   310   count

   311 }

   312 

   313 val A = (1 to 1000).toSet

   314 val B = (1 to 1000 by 4).toSet

   315 

   316 count_intersection(A, B)

   317 

   318 // but do not try to add .par to the for-loop above

   319 

   320 

   321 //propper parallel version

   322 def count_intersection2(A: Set[Int], B: Set[Int]) : Int = 

   323 	A.par.count(x => B contains x)

   324 

   325 count_intersection2(A, B)

   326 

   327 

   328 //for measuring time

   329 def time_needed[T](n: Int, code: => T) = {

   330   val start = System.nanoTime()

   331   for (i <- (0 to n)) code

   332   val end = System.nanoTime()

   333   (end - start) / 1.0e9

   334 }

   335 

   336 val A = (1 to 1000000).toSet

   337 val B = (1 to 1000000 by 4).toSet

   338 

   339 time_needed(10, count_intersection(A, B))

   340 time_needed(10, count_intersection2(A, B))

   341