エラトステネスのふるい実装してみた

eratosthenes.kt

fun main() {
    for (i in 3 until Int.MAX_VALUE step 1000) {
        val time = measureTimeMillis { eratosthenes(i) }
        println("$i : $time")
    }
//    eratosthenes(1000).forEachIndexed{i, isPrime -> println("$i : $isPrime")}

}

fun eratosthenes(n: Int) : Array<Boolean> {
    var numbers = arrayOf<Boolean>()
    for (i in 0 until n) {
        numbers += i % 2 != 0
    }
    numbers[1] = false
    numbers[2] = true
    for (i in 3..n+1 step 2) {
        if (i * i > n) {
            break
        }
        if (!numbers[i]) {
            continue
        }
        for (j in i*2 until n step i) {
            numbers[j] = false
        }
    }
    return numbers
}