Solution: Prime numbers sequence
val primes: Sequence<BigInteger> = sequence {
var i = BigInteger("2")
var primes = listOf(i)
yield(i)
while (true) {
i++
if (primes.none { i % it == BigInteger.ZERO }) {
primes += i
yield(i)
}
}
}
Example solution in playground
import org.junit.Test
import java.math.BigInteger
import kotlin.test.assertEquals
val primes: Sequence<BigInteger> = sequence {
var i = BigInteger("2")
var primes = listOf(i)
yield(i)
while (true) {
i++
if (primes.none { i % it == BigInteger.ZERO }) {
primes += i
yield(i)
}
}
}
class PrimesTest {
@Test
fun `should calculate the first 10 prime numbers`() {
val primes = primes.take(10).toList()
val expected = listOf(
BigInteger("2"),
BigInteger("3"),
BigInteger("5"),
BigInteger("7"),
BigInteger("11"),
BigInteger("13"),
BigInteger("17"),
BigInteger("19"),
BigInteger("23"),
BigInteger("29"),
)
assertEquals(expected, primes)
}
@Test(timeout = 1000)
fun `should calculate 1000'th prime number`() {
val prime = primes.drop(1000).first()
assertEquals(BigInteger("7927"), prime)
}
}
