/*
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).
*/
/**
* Transforms a string using the ROT13 substitution cipher.
*
* @param text - The input string to transform.
* @returns The transformed ROT13 string.
*/
function rot13(text: string): string {
if (typeof text !== 'string') {
throw new TypeError('Input must be a string');
}
// Use regex to match all alphabetic characters and replace them in-place
return text.replace(/[a-zA-Z]/g, (char: string): string => {
// Determine the ASCII base code ('A' is 65, 'a' is 97) with explicit typing
const base: number = char <= 'Z' ? 65 : 97;
// Extract character code and calculate shifted position explicitly
const charCode: number = char.charCodeAt(0);
const shiftedCode: number = ((charCode - base + 13) % 26) + base;
return String.fromCharCode(shiftedCode);
});
}
// Input string specified with an explicit type annotation
const message: string = "Hello, World! 123";
console.log(`Original: ${message}`);
// Apply ROT13 encryption
const encrypted: string = rot13(message);
console.log(`ROT13: ${encrypted}`);
// ROT13 is its own inverse; applying it again decrypts the message
const decrypted: string = rot13(encrypted);
console.log(`Decrypted: ${decrypted}`);
/*
run:
Original: Hello, World! 123
ROT13: Uryyb, Jbeyq! 123
Decrypted: Hello, World! 123
*/
