Exercise: Factorial sequence
Implement a program that calculates and displays the factorial of a given number. The factorial of a number is the product of all positive integers up to that number. So, the first 5 numbers in this sequence should be:
0! = 11! = 12! = 1 * 2 = 23! = 1 * 2 * 3 = 64! = 1 * 2 * 3 * 4 = 24
This sequence should be infinite. The result should be of type BigInteger.
val factorial: Sequence<BigInteger> = sequence {
TODO()
}
This problem can either be solved in the below playground or you can clone kotlin-exercises project and solve it locally. In the project, you can find code template for this exercise in coroutines/sequences/Factorial.kt. You can find there starting code and unit tests.
Once you are done with the exercise, you can check your solution here.
Playground
import org.junit.Test
import java.math.BigDecimal
import java.math.BigInteger
import kotlin.test.assertEquals
val factorial: Sequence<BigInteger> = sequence {
TODO()
}
class FactorialTest {
@Test
fun `should calculate factorial of first 10 numbers`() {
val factorials = factorial.take(10).toList()
val expected = listOf(
BigInteger.ONE,
BigInteger.ONE,
BigInteger("2"),
BigInteger("6"),
BigInteger("24"),
BigInteger("120"),
BigInteger("720"),
BigInteger("5040"),
BigInteger("40320"),
BigInteger("362880"),
)
assertEquals(expected, factorials)
}
@Test(timeout = 1000)
fun `should calculate factorial of 1000'th number`() {
val factorial = factorial.drop(1000).first()
assertEquals(BigInteger("402387260077093773543702433923003985719374864210714632543799910429938512398629020592044208486969404800479988610197196058631666872994808558901323829669944590997424504087073759918823627727188732519779505950995276120874975462497043601418278094646496291056393887437886487337119181045825783647849977012476632889835955735432513185323958463075557409114262417474349347553428646576611667797396668820291207379143853719588249808126867838374559731746136085379534524221586593201928090878297308431392844403281231558611036976801357304216168747609675871348312025478589320767169132448426236131412508780208000261683151027341827977704784635868170164365024153691398281264810213092761244896359928705114964975419909342221566832572080821333186116811553615836546984046708975602900950537616475847728421889679646244945160765353408198901385442487984959953319101723355556602139450399736280750137837615307127761926849034352625200015888535147331611702103968175921510907788019393178114194545257223865541461062892187960223838971476088506276862967146674697562911234082439208160153780889893964518263243671616762179168909779911903754031274622289988005195444414282012187361745992642956581746628302955570299024324153181617210465832036786906117260158783520751516284225540265170483304226143974286933061690897968482590125458327168226458066526769958652682272807075781391858178889652208164348344825993266043367660176999612831860788386150279465955131156552036093988180612138558600301435694527224206344631797460594682573103790084024432438465657245014402821885252470935190620929023136493273497565513958720559654228749774011413346962715422845862377387538230483865688976461927383814900140767310446640259899490222221765904339901886018566526485061799702356193897017860040811889729918311021171229845901641921068884387121855646124960798722908519296819372388642614839657382291123125024186649353143970137428531926649875337218940694281434118520158014123344828015051399694290153483077644569099073152433278288269864602789864321139083506217095002597389863554277196742822248757586765752344220207573630569498825087968928162753848863396909959826280956121450994871701244516461260379029309120889086942028510640182154399457156805941872748998094254742173582401063677404595741785160829230135358081840096996372524230560855903700624271243416909004153690105933983835777939410970027753472000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"), factorial)
}
}
