diff --git a/snippets/caesarCipher.md b/snippets/caesarCipher.md new file mode 100644 index 000000000..2a8e9397e --- /dev/null +++ b/snippets/caesarCipher.md @@ -0,0 +1,34 @@ +--- +title: caesarCipher +tags: algorithm,string,beginner +--- + +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 et.c +- 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!' +```