nbonacci sequence (n-bonacci数列)の初項から指定した数の項までを計算するためのScalaのコード例。

nbonacci.scala

//
// See https://pandanote.info/?p=6259 for details.
//

package info.pandanote.nbonaccitest

import scopt.OParser
import org.slf4j.LoggerFactory
import scala.collection.mutable.ListBuffer

case class Options(a: Int = 2, n: Int = 10)

class NBonacci

object NBonacci {
  private lazy val logger = LoggerFactory.getLogger(classOf[NBonacci])

  def main(args: Array[String]): Unit = {
    val builder = OParser.builder[Options]
    val parser = {
      import builder._
      OParser.sequence(
        programName("NBonacci"),
        head("NBonacci","0.1.0-SNAPSHOT"),
        opt[Int]('a',"term")
          .action((x,c) => c.copy(a = x)).text("Number of terms in the recurrence relation.")
          .validate(x =>
            if (x > 0) success
            else failure("Value <a> must be a positive integer")),
        opt[Int]('n',"number-of-terms")
          .action((x,c) => c.copy(n = x)).text("Number of terms to calculate.")
          .validate(x =>
            if (x > 0) success
            else failure("Value <n> must be a positive integer")),
        help("help").text("Calculate n-bonacci sequence.")
      )
    }

    val o: Options = OParser.parse(parser,args,Options()) match {
      case Some(options) => options
      case _ => sys.exit(1)
    }

    logger.info(o.toString)

    val buf = ListBuffer.fill(o.a-1)(0)
    buf += 1
    var count = 0
    while (count < o.n) {
      if (count < o.a) {
        println(buf(count))
      } else {
        val next = buf.result.foldRight(0){(x,y) => x+y}
        println(next)
        buf += next
        buf.remove(0)
      }
      count+=1
    }
  }
}