rot13.swift

// Playground - noun: a place where people can play

let lettersArray = Array("ABCDEFGHIJKLMNOPQRSTUVWXYZABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyz")

func rot13(input: String) -> String {
    return reduce(input, "") { result, letter in
        if let i = find(lettersArray, letter) {
            return result + lettersArray[i + 13]
        } else {
            return result + letter
        }
    }
}

rot13("Hello World!")