rot13.swift

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

import UIKit

let lettersArray = Array("ABCDEFGHIJKLMNOPQRSTUVWXYZABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyz")

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

rot13("rot13")