17 lines
917 B
Scala
17 lines
917 B
Scala
object TruncatablePrimes {
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def main(args: Array[String]): Unit = {
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val max = 1000000
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println(
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s"""|ltPrime: ${ltPrimes.takeWhile(_ <= max).last}
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|rtPrime: ${rtPrimes.takeWhile(_ <= max).last}
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|""".stripMargin)
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}
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def ltPrimes: LazyList[Int] = 2 #:: LazyList.from(3, 2).filter(isLeftTruncPrime)
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def rtPrimes: LazyList[Int] = 2 #:: LazyList.from(3, 2).filter(isRightTruncPrime)
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def isPrime(num: Int): Boolean = (num > 1) && !LazyList.range(3, math.sqrt(num).toInt + 1, 2).exists(num%_ == 0)
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def isLeftTruncPrime(num: Int): Boolean = !num.toString.contains('0') && Iterator.unfold(num.toString){str => if(str.nonEmpty) Some((str.toInt, str.tail)) else None}.forall(isPrime)
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def isRightTruncPrime(num: Int): Boolean = !num.toString.exists(_.asDigit%2 == 0) && Iterator.unfold(num.toString){str => if(str.nonEmpty) Some((str.toInt, str.init)) else None}.forall(isPrime)
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}
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