Fibonacci series in Swift

Fibonacci.swift

// Fibonacci series
// F[n] = F[n-1] + F[n-2]
// 0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144
// Find the fibonacci number for n interations

func fibonacci(n: Int) {

    var num1 = 0
    var num2 = 1

    for _ in 0 ..< n {
    
        let num = num1 + num2
        num1 = num2
        num2 = num
    }
    
    print("result = \(num2)")
}
fibonacci(7)


// Using Recursion
func fibonacciRecursiveNum1(num1: Int, num2: Int, steps: Int) {

    if steps > 0 {
        let newNum = num1 + num2
        fibonacciRecursiveNum1(num2, num2: newNum, steps: steps-1)
    }
    else {
        print("result = \(num2)")
    }
}
fibonacciRecursiveNum1(0, num2: 1, steps: 7)

taken from

func fib(_ N: Int) -> Int {
        
    // Init a bottom up array
    var bottomUp: [Int] = []
    
    /**
    Add the 3 known starting cases of 
    the fibonacci sequence
    */
    bottomUp.append(0)
    bottomUp.append(1)
    bottomUp.append(1)
    
    // Check that N is larger than 2
    if N > 2 {
        
        // If so, iterate up through N + 1
        for index in 3...N + 1 {

            // And calculate the fib for that spot
            bottomUp.append(bottomUp[index - 1] + bottomUp[index - 2])
        }
    }
    
    // Return the Nth fib
    return bottomUp[N]
}