merge: Add Affine Cipher (TheAlgorithms#1067)

* Add Affine Cipher * Replace IndexOf function to improve performance * remove leading spacing and fixed typo * Remove leading spacing in first row.

Author: shidian00

Ciphers/AffineCipher.js

@@ -0,0 +1,95 @@
+/**
+ * @description - The affine cipher is a type of monoalphabetic substitution cipher, where each letter in an alphabet is mapped to its numeric equivalent, encrypted using a simple mathematical function, and converted back to a letter
+ * @see - [wiki](https://en.wikipedia.org/wiki/Affine_cipher)
+ */
+
+// Default key for Affine Cipher
+constkey='ABCDEFGHIJKLMNOPQRSTUVWXYZ'
+
+/**
+ * Fix result for negative value in modulas equation
+ * @param{Number} n - Constant number
+ * @param{Number} m - Modulos value
+ * @return{Number} Return n mod m
+ */
+functionmod(n,m){
+return((n%m)+m)%m
+}
+
+/**
+ * Modular multiplicative inverse
+ * @param{Number} a - A coefficient
+ * @param{Number} m - Modulos value
+ * @return{Number} Return modular multiplicative inverse of coefficient a and modulos m
+ */
+functioninverseMod(a,m){
+for(letx=1;x<m;x++){
+if(mod(a*x,m)===1)returnx
+}
+}
+
+/**
+ * Argument validation
+ * @param{String} str - String to be checked
+ * @param{Number} a - A coefficient to be checked
+ * @param{Number} b - B coefficient to be checked
+ * @return{Boolean} Result of the checking
+ */
+functionisCorrectFormat(str,a,b){
+if(typeofa!=='number'||typeofb!=='number'){
+thrownewTypeError('Coefficient a, b should be number')
+}
+
+if(typeofstr!=='string'){
+thrownewTypeError('Argument str should be String')
+}
+
+returntrue
+}
+/**
+ * Find character index based on ASCII order
+ * @param{String} char - Character index to be found
+ * @return{Boolean} Character index
+ */
+functionfindCharIndex(char){
+returnchar.toUpperCase().charCodeAt(0)-('A').charCodeAt(0)
+}
+
+/**
+ * Encrypt a Affine Cipher
+ * @param{String} str - String to be encrypted
+ * @param{Number} a - A coefficient
+ * @param{Number} b - B coefficient
+ * @return{String} result - Encrypted string
+ */
+functionencrypt(str,a,b){
+letresult=''
+if(isCorrectFormat(str,a,b)){
+for(letx=0;x<str.length;x++){
+constcharIndex=findCharIndex(str[x])
+if(charIndex<0)result+='-1'+' '
+elseresult+=mod(a*charIndex+b,26)+' '
+}
+}
+returnresult.trim()
+}
+/**
+ * Decrypt a Affine Cipher
+ * @param{String} str - String to be decrypted
+ * @param{Number} a - A coefficient
+ * @param{Number} b - B coefficient
+ * @return{String} result - Decrypted string
+ */
+functiondecrypt(str,a,b){
+letresult=''
+if(isCorrectFormat(str,a,b)){
+str=str.split(' ')
+for(letx=0;x<str.length;x++){
+if(str[x]==='-1')result+=' '
+elseresult+=key[mod(inverseMod(a,26)*(parseInt(str[x])-b),26)]
+}
+}
+returnresult
+}
+
+export{encrypt,decrypt}

Ciphers/test/AffineCipher.test.js

@@ -0,0 +1,27 @@
+import{encrypt,decrypt}from'../AffineCipher'
+
+describe('Test Affine Cipher',()=>{
+it('Test - 1, Pass invalid input to encrypt function',()=>{
+expect(()=>encrypt(null,null,null)).toThrow()
+expect(()=>encrypt('null',null,null)).toThrow()
+expect(()=>encrypt('null',1,null)).toThrow()
+expect(()=>encrypt('null',null,1)).toThrow()
+})
+
+it('Test - 2, Pass invalid input to decrypt function',()=>{
+expect(()=>decrypt(null,null,null)).toThrow()
+expect(()=>decrypt('null',null,null)).toThrow()
+expect(()=>decrypt('null',1,null)).toThrow()
+expect(()=>decrypt('null',null,1)).toThrow()
+})
+
+it('Test - 3 Pass string value to encrypt and ecrypt function',()=>{
+consta=5
+constb=8
+expect(decrypt(encrypt('HELLO WORLD',a,b),a,b)).toBe('HELLO WORLD')
+expect(decrypt(encrypt('ABC DEF',a,b),a,b)).toBe('ABC DEF')
+expect(decrypt(encrypt('Brown fox jump over the fence',a,b),a,b)).toBe(
+'BROWN FOX JUMP OVER THE FENCE'
+)
+})
+})