Returns the nth number in the Fibonacci Sequence.

IterativeNthFibonacci.swift

func iterativeFib(_ n: Int) -> Int {
    var n1 = 1, n2 = 1, answer = 0, temp = 0
    for _ in 2..<n {
        answer = n1 + n2
        temp = n2
        n2 = answer
        n1 = temp
    }
    return answer
}