almost no size limit fact compute / published by https://github.com/dacr/code-examples-manager #0eba7267-0982-4f39-bb40-3c3b1e723336/a2f1c3892e82cab8467f42c2515ad5d0fc663e4f

math-fact.sc

// summary : almost no size limit fact compute
// keywords : scala, math, fact, @testable
// publish : gist
// authors : David Crosson
// license : Apache NON-AI License Version 2.0 (https://raw.githubusercontent.com/non-ai-licenses/non-ai-licenses/main/NON-AI-APACHE2)
// id : 0eba7267-0982-4f39-bb40-3c3b1e723336
// created-on : 2020-12-14T05:51:15Z
// managed-by : https://github.com/dacr/code-examples-manager
// run-with : scala-cli $file

// ---------------------
//> using scala  "3.3.0"
//> using dep "org.scalatest::scalatest:3.2.16"
//> using objectWrapper
// ---------------------

import org.scalatest.*
import flatspec.*
import matchers.*

import scala.annotation.tailrec



@tailrec
def fact(x: Int, accu: BigInt = 1): BigInt =
  if (x <= 1) accu else fact(x - 1, accu * x)

def factClassic(n: BigInt): BigInt =
  if (n <= 1) 1 else n*factClassic(n - 1)

def factAlt(num: Int): BigInt = {
  LazyList
    .from(1)
    .take(num)
    .map(x => BigInt(x))
    .foldLeft(BigInt(1)) {case (a,b) => a * b}
}

class FactTest extends AnyFlatSpec with should.Matchers {
  override def suiteName: String = "FactTest"

  "fact" should "return the right result" in {
    fact(0) shouldBe 1
    fact(1) shouldBe 1
    fact(2) shouldBe 2
    fact(3) shouldBe 6
    fact(4) shouldBe 24
    fact(42) shouldBe BigInt("1405006117752879898543142606244511569936384000000000")
  }
}

org.scalatest.tools.Runner.main(Array("-oDF", "-s", classOf[FactTest].getName))