/*
ROT13 is a simple substitution cipher that replaces a letter with the 13th letter
after it in the alphabet. Because the English alphabet has 26 letters (13 * 2),
applying ROT13 twice restores the original text (it is its own inverse).
*/
package main
import (
"fmt"
"strings"
)
// rot13Rune applies the ROT13 transformation logic to an individual rune.
func rot13Rune(r rune) rune {
switch {
case r >= 'a' && r <= 'z':
// Shift lowercase letters by 13, wrapping around with modulo 26
return 'a' + (r-'a'+13)%26
case r >= 'A' && r <= 'Z':
// Shift uppercase letters by 13, wrapping around with modulo 26
return 'A' + (r-'A'+13)%26
default:
// Non-alphabetic characters (digits, spaces, punctuation) pass through untouched
return r
}
}
// rot13 transforms an input string using the ROT13 substitution cipher.
func rot13(text string) string {
// strings.Map efficiently applies a mapping function to all characters (runes) in the string
return strings.Map(rot13Rune, text)
}
func main() {
// Input string specified
message := "Hello, World! 123"
fmt.Printf("Original: %s\n", message)
// Apply ROT13 encryption
encrypted := rot13(message)
fmt.Printf("ROT13: %s\n", encrypted)
// ROT13 is its own inverse; applying it again decrypts the message
decrypted := rot13(encrypted)
fmt.Printf("Decrypted: %s\n", decrypted)
}
/*
run:
Original: Hello, World! 123
ROT13: Uryyb, Jbeyq! 123
Decrypted: Hello, World! 123
*/
