Swift ROT13

ROT13.swift

var rot13key = [Character:Character]()
let uppercase = Array("ABCDEFGHIJKLMNOPQRSTUVWXYZ")
let lowercase = Array("abcdefghijklmnopqrstuvwxyz")
for var i = 0; i < 26; i++ {
    rot13key[uppercase[i]] = uppercase[(i + 13) % 26]
    rot13key[lowercase[i]] = lowercase[(i + 13) % 26]
}

func rot13(s: String) -> String {
    return String(seq: map(s, { rot13key[$0] ?? $0 }))
}