39 lines
1.3 KiB
Markdown
39 lines
1.3 KiB
Markdown
---
|
|
title: Caesar cipher
|
|
type: snippet
|
|
language: javascript
|
|
tags: [algorithm,string]
|
|
cover: ancient-greek-building
|
|
dateModified: 2020-12-29T12:29:21+02:00
|
|
---
|
|
|
|
Encrypts or decrypts a given string using the Caesar cipher.
|
|
|
|
- Use the modulo (`%`) operator and the ternary operator (`?`) to calculate the correct encryption/decryption key.
|
|
- Use the spread operator (`...`) and `Array.prototype.map()` to iterate over the letters of the given string.
|
|
- Use `String.prototype.charCodeAt()` and `String.fromCharCode()` to convert each letter appropriately, ignoring special characters, spaces etc.
|
|
- Use `Array.prototype.join()` to combine all the letters into a string.
|
|
- Pass `true` to the last parameter, `decrypt`, to decrypt an encrypted string.
|
|
|
|
```js
|
|
const caesarCipher = (str, shift, decrypt = false) => {
|
|
const s = decrypt ? (26 - shift) % 26 : shift;
|
|
const n = s > 0 ? s : 26 + (s % 26);
|
|
return [...str]
|
|
.map((l, i) => {
|
|
const c = str.charCodeAt(i);
|
|
if (c >= 65 && c <= 90)
|
|
return String.fromCharCode(((c - 65 + n) % 26) + 65);
|
|
if (c >= 97 && c <= 122)
|
|
return String.fromCharCode(((c - 97 + n) % 26) + 97);
|
|
return l;
|
|
})
|
|
.join('');
|
|
};
|
|
```
|
|
|
|
```js
|
|
caesarCipher('Hello World!', -3); // 'Ebiil Tloia!'
|
|
caesarCipher('Ebiil Tloia!', 23, true); // 'Hello World!'
|
|
```
|