merge: Improved CaesarsCipher Algorithm (TheAlgorithms#963)

* chore: added helper variable * feat: added new rotation option * Revert "chore: added helper variable" This reverts commit 489544d.

Author: fahimfaisaal

Ciphers/CaesarsCipher.js

@@ -1,35 +1,32 @@
 /**
- * Caesar's Cipher - also known as the ROT13 Cipher is when
- * a letter is replaced by the one that is 13 spaces away
- * from it in the alphabet. If the letter is in the first half
- * of the alphabet we add 13, if it's in the latter half we
- * subtract 13 from the character code value.
+ * @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 caesarsCipher = (str, rotation) => {
+ if (typeof str !== 'string' || !Number.isInteger(rotation) || rotation < 0) {
+ throw new TypeError('Arguments are invalid')
+ }
 
-/**
- * Decrypt a ROT13 cipher
- * @param {String} str - string to be decrypted
- * @return {String} decrypted string
- */
-function rot13 (str) {
- const response = []
- const strLength = str.length
+ const alphabets = new Array(26)
+ .fill()
+ .map((_, index) => String.fromCharCode(97 + index)) // generate all lower alphabets array a-z
 
- for (let i = 0; i < strLength; i++) {
- const char = str.charCodeAt(i)
+ const cipherMap = alphabets.reduce(
+ (map, char, index) => map.set(char, alphabets[(rotation + index) % 26]),
+ new Map()
+ )
 
- if (char < 65 || (char > 90 && char < 97) || char > 122) {
- response.push(str.charAt(i))
- } else if ((char > 77 && char <= 90) || (char > 109 && char <= 122)) {
- response.push(String.fromCharCode(str.charCodeAt(i) - 13))
- } else {
- response.push(String.fromCharCode(str.charCodeAt(i) + 13))
+ return str.replace(/[a-z]/gi, (char) => {
+ if (/[A-Z]/.test(char)) {
+ return cipherMap.get(char.toLowerCase()).toUpperCase()
  }
- }
- return response.join('')
-}
 
-export { rot13 }
+ return cipherMap.get(char)
+ })
+}
 
-// > rot13('Uryyb Jbeyq')
-// 'Hello World'
+export default caesarsCipher

Ciphers/test/CaesarsCipher.test.js

@@ -0,0 +1,16 @@
+import caesarsCipher from '../CaesarsCipher'
+
+describe('Testing the caesarsCipher function', () => {
+ it('Test - 1, Testing for invalid types', () => {
+ expect(() => caesarsCipher(false, 3)).toThrow()
+ expect(() => caesarsCipher('false', -1)).toThrow()
+ expect(() => caesarsCipher('true', null)).toThrow()
+ })
+
+ it('Test - 2, Testing for valid string and rotation', () => {
+ expect(caesarsCipher('middle-Outz', 2)).toBe('okffng-Qwvb')
+ expect(caesarsCipher('abcdefghijklmnopqrstuvwxyz', 3)).toBe('defghijklmnopqrstuvwxyzabc')
+ expect(caesarsCipher('Always-Look-on-the-Bright-Side-of-Life', 5)).toBe('Fqbfdx-Qttp-ts-ymj-Gwnlmy-Xnij-tk-Qnkj')
+ expect(caesarsCipher('THE QUICK BROWN FOX JUMPS OVER THE LAZY DOG', 23)).toBe('QEB NRFZH YOLTK CLU GRJMP LSBO QEB IXWV ALD')
+ })
+})