Fibonacci Functions

package io.github.cjwebb

import scala.annotation.tailrec

object Fibonacci extends App {

  /** Get the nth fibonacci number */
  def fib_iter(n: Int) = {
    if (n < 2) n
    else {
      var ans = 0
      var n1 = 0
      var n2 = 1

      var i = n - 1
      while (i > 0) {
        i = i - 1
        ans = n1 + n2
        n1 = n2
        n2 = ans
      }
      ans
    }
  }

  def fib_recur(n: Int): Int = {
    n match {
      case i if i < 2 => i
      case i => fib_recur(n-1) + fib_recur(n-2)
    }
  }

  def fib_tailrec(n: Int) = {
    @tailrec
    def rec(n: Int, a: Int, b: Int): Int= {
      n match {
        case 0 => b
        case _ => rec(n-1, a+b, a)
      }
    }
    rec(n, 1, 0)
  }

  
  /** Pass in n, to receive that many numbers */  
  def bad_fib(n: Int) = (0 to n-1) map (n => fib_tailrec(n))
  
  def fib_acc(n: Int) = {
    @tailrec
    def acc(list: List[Int], i: Int): List[Int] = {
      if (i >= n || n < 2) list
      else {
        val newList = list ::: List(list(i-1)+list(i-2))
        acc(newList, i+1)
      }
    }

    acc(List(0, 1), 2).take(n)
  }

  def fib_acc2(n: Int, s: List[Int] = List(1, 0)): List[Int] = {
    if (n <= 2) s.reverse
    else fib_acc2(n - 1, s(0) + s(1) :: s)
  }

  def fib_stream(n: Int) = {
    lazy val fibs: Stream[Int] = 0 #:: fibs.scanLeft(1)(_ + _)
    fibs.take(n).toList
  }


  println((0 to 10) map (n => fib_recur(n)))
  println((0 to 10) map (n => fib_iter(n)))
  println((0 to 10) map (n => fib_tailrec(n)))
  println(fib_acc2(10))
  println(fib_stream(10))

}