281 

   282 

   283 // Avoid being mutable

   284 //=====================

   285 

   286 // a student showed me...

   287 import scala.collection.mutable.ListBuffer

   288 

   289 def collatz_max(bnd: Long): (Long, Long) = {

   290   val colNos = ListBuffer[(Long, Long)]()

   291   for (i <- (1L to bnd).toList) colNos += ((collatz(i), i))

   292   colNos.max

   293 }

   294 

   295 def collatz_max(bnd: Long): (Long, Long) = {

   296   (1L to bnd).map((i) => (collatz(i), i)).maxBy(_._1)

   297 }

   298 

   299 //views -> lazy collection

   300 def collatz_max(bnd: Long): (Long, Long) = {

   301   (1L to bnd).view.map((i) => (collatz(i), i)).maxBy(_._1)

   302 }

   303 

   304 // raises a GC exception

   305 (1 to 1000000000).filter(_ % 2 == 0).take(10).toList

   306 // ==> java.lang.OutOfMemoryError: GC overhead limit exceeded

   307 

   308 (1 to 1000000000).view.filter(_ % 2 == 0).take(10).toList