rot13 in Swift 3

rot13_Swift3.txt

// rot 13

var rot13Mapped = [Character:Character]()

let upperCase = Array("ABCDEFGHIJKLMNOPQRSTUVWXYZ".characters)
let lowerCase = Array("abcdefghijklmnopqrstuvwxyz".characters)

for (index, _) in upperCase.enumerated() {
    rot13Mapped[upperCase[index]] = upperCase[(index + 13) % 26]
    rot13Mapped[lowerCase[index]] = lowerCase[(index + 13) % 26]
}

func rot13(forString string: String) -> String {
    return String(string.characters.map { rot13Mapped[$0] ?? $0 })
}

print(rot13(forString: "Pete"))