mirror of
https://github.com/TheAlgorithms/JavaScript.git
synced 2025-07-05 08:16:50 +08:00
33 lines
1.4 KiB
JavaScript
33 lines
1.4 KiB
JavaScript
/**
|
|
* @function caesarsCipher
|
|
* @description - In cryptography, a Caesar cipher, also known as Caesar's cipher, the shift cipher, Caesar's code or Caesar shift, is one of the simplest and most widely known encryption techniques. It is a type of substitution cipher in which each letter in the plaintext is replaced by a letter some fixed number of positions down the alphabet. For example, with a left shift of 3, D would be replaced by A, E would become B, and so on. The method is named after Julius Caesar, who used it in his private correspondence.
|
|
* @see - [wiki](https://en.wikipedia.org/wiki/Caesar_cipher)
|
|
* @param {string} str - string to be encrypted
|
|
* @param {number} rotation - the number of rotation, expect real number ( > 0)
|
|
* @return {string} - decrypted string
|
|
*/
|
|
const caesarCipher = (str, rotation) => {
|
|
if (typeof str !== 'string' || !Number.isInteger(rotation) || rotation < 0) {
|
|
throw new TypeError('Arguments are invalid')
|
|
}
|
|
|
|
const alphabets = new Array(26)
|
|
.fill()
|
|
.map((_, index) => String.fromCharCode(97 + index)) // generate all lower alphabets array a-z
|
|
|
|
const cipherMap = alphabets.reduce(
|
|
(map, char, index) => map.set(char, alphabets[(rotation + index) % 26]),
|
|
new Map()
|
|
)
|
|
|
|
return str.replace(/[a-z]/gi, (char) => {
|
|
if (/[A-Z]/.test(char)) {
|
|
return cipherMap.get(char.toLowerCase()).toUpperCase()
|
|
}
|
|
|
|
return cipherMap.get(char)
|
|
})
|
|
}
|
|
|
|
export default caesarCipher
|