37 lines
1.3 KiB
Markdown
37 lines
1.3 KiB
Markdown
---
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title: caesarCipher
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tags: algorithm,string,beginner
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firstSeen: 2020-12-28T20:10:18+02:00
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lastUpdated: 2020-12-29T12:29:21+02:00
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---
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Encrypts or decrypts a given string using the Caesar cipher.
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- Use the modulo (`%`) operator and the ternary operator (`?`) to calculate the correct encryption/decryption key.
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- Use the spread operator (`...`) and `Array.prototype.map()` to iterate over the letters of the given string.
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- Use `String.prototype.charCodeAt()` and `String.fromCharCode()` to convert each letter appropriately, ignoring special characters, spaces etc.
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- Use `Array.prototype.join()` to combine all the letters into a string.
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- Pass `true` to the last parameter, `decrypt`, to decrypt an encrypted string.
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```js
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const caesarCipher = (str, shift, decrypt = false) => {
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const s = decrypt ? (26 - shift) % 26 : shift;
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const n = s > 0 ? s : 26 + (s % 26);
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return [...str]
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.map((l, i) => {
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const c = str.charCodeAt(i);
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if (c >= 65 && c <= 90)
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return String.fromCharCode(((c - 65 + n) % 26) + 65);
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if (c >= 97 && c <= 122)
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return String.fromCharCode(((c - 97 + n) % 26) + 97);
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return l;
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})
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.join('');
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};
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```
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```js
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caesarCipher('Hello World!', -3); // 'Ebiil Tloia!'
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caesarCipher('Ebiil Tloia!', 23, true); // 'Hello World!'
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```
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