It doesnt look so pretty but it works. I dont understand why I needed to 'hack' this to make it work though, obviously I started with fib 0 and 1 = to 1 but had to 'hack' it since it was off by 2

Haskell:

fib 0 = 0
fib 1 = 0
fib 2 = 1
fib 3 = 1
fib n = fib (n-1) + fib (n-2)

It's sad that for each challenge the majority of comments take the form:

Why is ---------- language not on the list.
OR Please enable ----------- language.

Moderators should make some kind of Disclaimer or something about this.

based on the classics of Scala Stream API example:

lazy val fibSteam:Stream[Int] = 0 #:: 1 #:: fibSteam.zip(fibSteam.tail).map( x => x._1 + x._2 )

fibSteam.take(x).last

Elixir solution of the 'Fibonacci Numbers'

defmodule Solution do
  def fibonacci_n(n \\ 0) do
    case n do
      1 -> 0
      2 -> 1
      n -> fibonacci_n(n-1) + fibonacci_n(n-2)
    end
  end

  def main do
    IO.gets("") |> String.trim |> String.to_integer |> fibonacci_n |> IO.puts
  end
end

Solution.main

Some ugly Clojure:

(println ((fn fibs [num] (let [sum 0] (if (= 1 num) 0 (if (= 2 num) 1 (+ (fibs (dec num)) (fibs (- num 2))))))) (Integer/parseInt (clojure.string/trim (read-line)))))

Would this be possible using Clojure's loop-recur functions? I played with a bit and decided it couldn't be done, anbody have any insights on whether that is accurate?

Looks a bit hacky but simple. Scala.

     def fibonacci(x:Int):Int = {
         if(x <= 1) x
         else {
          (1 to x-1).foldLeft((0, 1)) {
              case ((a,b), i) => (b, a+b)
          }._1
         }
     }

Tail recursive in Scala

def fibonacci(x: Int): Int = {
    val initialValue = 0 // f(1) == 0
    val initNext = 1 // f(2) == 1
    val initialIndex = 1 // 1 < N <= 40
    @tailrec
    def iter(cur: Int, next: Int, acc: Int): Int = {
        if (acc == x) cur
        else iter(next, cur + next, acc + 1)
    }
    iter(initialValue, initialNext, initialIndex)
}

fibh :: Int -> Int -> Int -> Int
fibh 1 a b = a+b
fibh n a b = fibh (n-1) b (a+b)

fib 1 = 0
fib 2 = 1
fib n = fibh (n-2) 0 1

i feel dirty for using recursion like this, but the runtime should be fine...

What's wrong with this code??

def fibonacci(n : Int) : Long = { if( n == 0 ){ return 0; } else if( n == 1 ){ return 1; } else{ return fibonacci(n-1) + fibonacci(n-2); } }