HelloWorld.scala

package helloworld

import scala.collection.immutable.LinearSeq
import scala.annotation.tailrec
import scala.util.Random
import scala.collection.mutable.MutableList
import scala.collection.immutable.Queue

object HelloWorld {
  
  def getArray() : Array[Int] = {
    val ar = new Array[Int](20000)
    
    for (i <- 0 until ar.length) {
      ar(i) = i
    }
    
    ar
  }
  def getList() : LinearSeq[Int] = {
    var lst = Queue[Int]()
    
    for (i <- 0 until 20000) {
      lst = lst.enqueue(-i)
    }
    
    lst
  }
  
  def main(args: Array[String]) = {
    val array = getList()
    val now = System.nanoTime
    val result = isSorted2(array, (x: Int, y: Int) => x < y)
    val elapsedTime = System.nanoTime - now
    println(result)
    println("Took %d ms.".format(elapsedTime / 1000000))
  }
  
  def isSorted1[A](items: Array[A], cond: (A, A) => Boolean): Boolean = items match {
    case Array(_) => true
    case Array(x, y) => cond(x, y)
    case Array(_*) => cond(items(0), items(1)) && isSorted1(items tail, cond)
  }

  @tailrec // remind the compiler that the recursion can be eliminated
  def isSorted2[A](items: LinearSeq[A], cond: (A, A) => Boolean): Boolean = items match {
    case Seq() => true // you forgot to handle empty input!
    case Seq(_) => true
    case x :: tail => cond(x, tail.head) && isSorted2(tail, cond)
  }
  
  def isSorted3[A](items: Iterable[A], cond: (A, A) => Boolean): Boolean =
  items.isEmpty || (items zip items.tail forall (pair => cond(pair._1, pair._2)))
}