Fibonacci

fibonacci.swift

func fibonacciRecursive(_ index: Int) -> Int {
    if index < 2 {
        return index
    }
    return fibonacciRecursive(index - 2) + fibonacciRecursive(index - 1)
}

func fibonacciIterative(_ index: Int) -> Int {
    if index < 2 {
        return index
    }
    var result = 0
    var prev = 1
    var prevPrev = 1
    for _ in 2...index {
        result = prev + prevPrev
        prevPrev = prev
        prev = result
    }
    return result
}