cipher.swift

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

import Darwin

let alphabets: [[Character]] = [
    ["a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l", "m", "n", "o", "p", "q", "r", "s", "t", "u", "v", "w", "x", "y", "z"],
    ["A", "B", "C", "D", "E", "F", "G", "H", "I", "J", "K", "L", "M", "N", "O", "P", "Q", "R", "S", "T", "U", "V", "W", "X", "Y", "Z"]
]

func cipherWithRotation(rotation: Int) -> [Character: Character] {
    var cipher = [Character: Character]()
    for alphabet in alphabets {
        for index in (0..<(alphabet.count)) {
            cipher[alphabet[index]] = alphabet[(index + rotation) % alphabet.count]
        }
    }
    return cipher
}

func cipherString(str: String, rotation: Int) -> String {
    let cipher = cipherWithRotation(rotation)
    return String(str.characters.map { cipher[$0] ?? $0 })
}

let input = "The quick brown fox jumped over the lazy dog."
let cipherText = cipherString(input, rotation: 13)
let decipherText = cipherString(cipherText, rotation: 13)