CaeserCipher.swift

import Foundation;

_ = readLine()! // irrelavent
let S = readLine()!
let K = Int(readLine()!)!

// MARK: - Encryption Function
func encryptString(_ string: String, rotation: Int) -> String {
    var encryptedString = String()
    for char in string.unicodeScalars {
        var code = Int(char.value)
        // is lowercased letter
        if (97...122).contains(char.value) {
            code += rotation
            while (code > 122) {
                // reduce until in char range
                code -= (122 - 96)
            }
        // is uppercased letter
        } else if (65...90).contains(char.value) {
            code += rotation
            while (code > 90) {
                // reduce until in char range
                code -= (90 - 64)
            }
        }
        encryptedString += String(Character(UnicodeScalar(code)!))
    }
    return encryptedString
}

// encrypt string
print(encryptString(S, rotation: K))