scala-first-homework.scala

import scala.annotation.tailrec
import java.io.File

object FirstHomework extends App {
  
  //homework sum 1 to n using recursion
  def sumN(n: Int) = {
    @tailrec
    def sum(c: Int, acc: Int): Int = {
      if(c == 0) acc
      else sum(c - 1, c + acc)
    }
    sum(n, 0)
  }
  
  def listFiles(src: File): Array[File] = {
    val these = src.listFiles()
    these.filter(_.isFile()) ++ these.filter(_.isDirectory()).flatMap(listFiles)
  }
  
  def listFiles2(src: File) = {
    @tailrec
    def go(current: List[File], result: List[File]): List[File] = current match {
      case head::tail =>
        if(head.isFile()) go(tail, result:+head)
        else go(tail ++ head.listFiles(), result)
      case _ => result
    }
    go(src::Nil, Nil)
  }
  
}