factorial.swift

factorial.swift

func factorial(a: Int) -> Int {
    let n = a
    if(n == 1){
      return 1
    }else{
      return n*factorial(n-1)
    }
}

factorial(5)
factorial(6)

func factorial2(a: Int) -> Int {
    return a == 1 ? a : a*factorial(a-1)
}

factorial2(5)
factorial2(6)

func factorial(_ num: UInt) -> UInt {
    guard num != 0 else {
        return 1
    }

    return (1...num).reduce(1, { $0 * $1 })
}

factorial(0) // 1
factorial(5) // 120

Recursion is for hipsters 😜

Note the use of UInt, as factorials are only for positive numbers.

func factorial(_ n: Int) -> Double { return (1...n).map(Double.init).reduce(1.0, *) }