フィボナッチ数列

Fibonacci.swift

// インデックス番号を入れたらその番号のフィボナッチ数を出力
func fib(index: Int) -> Int {
    guard index > 1 else { return 1 }
    var a = 1
    var b = 1
    (2...index).forEach { (index) in
        (a, b) = (a + b, a)
    }

    return a

}

(0...10).forEach { (index) in
    print(fib5(index: index))
}
//出力
//1
//1
//2
//3
//5
//8
//13
//21
//34
//55
//89

// インデックス番号を入れたらそれまでのフィボナッチ数列を出力
func fibSequence(index: Int) {
    guard index > 1 else {
        print("1")
        return
    }

    var fibArray = [1, 1]
    (2...index).forEach { (index) in
        fibArray.append(fibArray[index-2] + fibArray[index-1])
    }

    let sequence = fibArray.reduce("") { (result, value) -> String in
        if result.isEmpty {
            return "\(value)"
        } else {
            return "\(result),\(value)"
        }
    }
    print(sequence)
}

fibSequence(index: 16)
// -> 1,1,2,3,5,8,13,21,34,55,89,144,233,377,610,987,1597