object Euler21 extends Application {
def sumdiv (n :Int) = List.range(1, n/2+1).filter(div => n % div == 0).foldLeft(0)(_+_)
println(List.range(1, 10000).filter(n => {
val sdn = sumdiv(n); (n == sumdiv(sdn) && n != sdn && sdn < 10000)
}).foldLeft(0)(_+_));
}This one is almost readable — if you've been staring at a lot of Scala recently. It also uses a less efficient method for computing divisors because it fits on one line.
The above runs in 1176ms but the version using:
def sumdiv (x :Int) = (1 :: List.flatten(for {
divis < - List.range(2, Math.sqrt(x)+1)
if x % divis == 0
} yield List(divis, x / divis).removeDuplicates)).foldLeft(0)(_+_)runs in 157ms. Oh the sacrifices we make for brevity.