I am new to Scala, just started learning, so this is basic beginner question.
I try to implement Sieve of Eratosthenes algorithm. Here is what I got so far:
def sieve_core(cross: Int, lst: Seq[Int]): List[Int] = { val crossed = lst.filter(_ % cross != 0) crossed match { case a :: rest => cross :: sieve_core(a, crossed) case _ => cross :: Nil } } def sieve(max: Int): List[Int] = { sieve_core(2, (2 to max)) } println(sieve(100))
The result is:
List(2)
As far as I understand, case _ => cross :: Nil
is matched in first iteration of sieve_core
, which means that crossed
is not an instance of a List.
I changed lst
parameters type to List[Int]
and now the code won't compile with an error:
(fragment of Problem3.scala):24: error: type mismatch; found : Range.Inclusive required: List[Int] sieve_core(2, (2 to max)) ^
Apparently Range
is not a List
.
Question: how can I turn Range into a List? Or is it some bigger problem with my code, I have made some bad assumption somewhere along the way?
Any help appreciated.
There's an apply
method on the List
companion object which takes a range and returns a List
:
scala> List.range(2, 11)
res0: List[Int] = List(2, 3, 4, 5, 6, 7, 8, 9, 10)
There are lots of useful List
factory methods in the List
collection documentation.
To turn any sequence s
into a list, use s.toList
I'm sure digitalross' is more efficient in this case, though.
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