From 7d40bb4a29d64834d17c9d554a52b5742a176dc2 Mon Sep 17 00:00:00 2001
From: shidian00 <81557908+shidian00@users.noreply.github.com>
Date: Wed, 27 Jul 2022 20:01:11 +0800
Subject: [PATCH 1/2] merge: Add Affine Cipher (#1067)

* Add Affine Cipher

* Replace IndexOf function to improve performance

* remove leading spacing and fixed typo

* Remove leading spacing in first row.
---
 Ciphers/AffineCipher.js           | 95 +++++++++++++++++++++++++++++++
 Ciphers/test/AffineCipher.test.js | 27 +++++++++
 2 files changed, 122 insertions(+)
 create mode 100644 Ciphers/AffineCipher.js
 create mode 100644 Ciphers/test/AffineCipher.test.js

diff --git a/Ciphers/AffineCipher.js b/Ciphers/AffineCipher.js
new file mode 100644
index 0000000000..367cb18597
--- /dev/null
+++ b/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
+const key = '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
+ */
+function mod (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
+ */
+function inverseMod (a, m) {
+  for (let x = 1; x < m; x++) {
+    if (mod(a * x, m) === 1) return x
+  }
+}
+
+/**
+ * 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
+ */
+function isCorrectFormat (str, a, b) {
+  if (typeof a !== 'number' || typeof b !== 'number') {
+    throw new TypeError('Coefficient a, b should be number')
+  }
+
+  if (typeof str !== 'string') {
+    throw new TypeError('Argument str should be String')
+  }
+
+  return true
+}
+/**
+ * Find character index based on ASCII order
+ * @param {String} char - Character index to be found
+ * @return {Boolean} Character index
+ */
+function findCharIndex (char) {
+  return char.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
+ */
+function encrypt (str, a, b) {
+  let result = ''
+  if (isCorrectFormat(str, a, b)) {
+    for (let x = 0; x < str.length; x++) {
+      const charIndex = findCharIndex(str[x])
+      if (charIndex < 0) result += '-1' + ' '
+      else result += mod(a * charIndex + b, 26) + ' '
+    }
+  }
+  return result.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
+ */
+function decrypt (str, a, b) {
+  let result = ''
+  if (isCorrectFormat(str, a, b)) {
+    str = str.split(' ')
+    for (let x = 0; x < str.length; x++) {
+      if (str[x] === '-1') result += ' '
+      else result += key[mod(inverseMod(a, 26) * (parseInt(str[x]) - b), 26)]
+    }
+  }
+  return result
+}
+
+export { encrypt, decrypt }
diff --git a/Ciphers/test/AffineCipher.test.js b/Ciphers/test/AffineCipher.test.js
new file mode 100644
index 0000000000..632704bce2
--- /dev/null
+++ b/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', () => {
+    const a = 5
+    const b = 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'
+    )
+  })
+})

From 1a089cc49122f558fb23fe0447637db1c9c2a721 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Lars=20M=C3=BCller?=
 <34514239+appgurueu@users.noreply.github.com>
Date: Wed, 27 Jul 2022 15:13:07 +0200
Subject: [PATCH 2/2] merge: Fix GetEuclidGCD (#1068)

* Fix GetEuclidGCD

Implement the actual Euclidean Algorithm

* Replace == with ===

* Lua > JS

* Standard sucks

* Oops

* Update GetEuclidGCD.js

* Updated Documentation in README.md

Co-authored-by: github-actions <${GITHUB_ACTOR}@users.noreply.github.com>
---
 DIRECTORY.md          |  1 +
 Maths/GetEuclidGCD.js | 42 +++++++++++++++---------------------------
 2 files changed, 16 insertions(+), 27 deletions(-)

diff --git a/DIRECTORY.md b/DIRECTORY.md
index 3793104e27..5a491bf570 100644
--- a/DIRECTORY.md
+++ b/DIRECTORY.md
@@ -18,6 +18,7 @@
 * **Cellular-Automata**
   * [ConwaysGameOfLife](Cellular-Automata/ConwaysGameOfLife.js)
 * **Ciphers**
+  * [AffineCipher](Ciphers/AffineCipher.js)
   * [Atbash](Ciphers/Atbash.js)
   * [CaesarsCipher](Ciphers/CaesarsCipher.js)
   * [KeyFinder](Ciphers/KeyFinder.js)
diff --git a/Maths/GetEuclidGCD.js b/Maths/GetEuclidGCD.js
index 3aff8dbbeb..aa77acbcc1 100644
--- a/Maths/GetEuclidGCD.js
+++ b/Maths/GetEuclidGCD.js
@@ -1,32 +1,20 @@
-/*
-    Problem statement and Explanation : https://en.wikipedia.org/wiki/Euclidean_algorithm
-
-    In this method, we have followed the iterative approach to first
-    find a minimum of both numbers and go to the next step.
-*/
-
 /**
- * GetEuclidGCD return the gcd of two numbers using Euclidean algorithm.
- * @param {Number} arg1 first argument for gcd
- * @param {Number} arg2 second argument for gcd
- * @returns return a `gcd` value of both number.
+ * GetEuclidGCD Euclidean algorithm to determine the GCD of two numbers
+ * @param {Number} a integer (may be negative)
+ * @param {Number} b integer (may be negative)
+ * @returns {Number} Greatest Common Divisor gcd(a, b)
  */
-const GetEuclidGCD = (arg1, arg2) => {
-  // firstly, check that input is a number or not.
-  if (typeof arg1 !== 'number' || typeof arg2 !== 'number') {
-    return new TypeError('Argument is not a number.')
+export function GetEuclidGCD (a, b) {
+  if (typeof a !== 'number' || typeof b !== 'number') {
+    throw new TypeError('Arguments must be numbers')
   }
-  // check that the input number is not a negative value.
-  if (arg1 < 1 || arg2 < 1) {
-    return new TypeError('Argument is a negative number.')
+  if (a === 0 && b === 0) return undefined // infinitely many numbers divide 0
+  a = Math.abs(a)
+  b = Math.abs(b)
+  while (b !== 0) {
+    const rem = a % b
+    a = b
+    b = rem
   }
-  // Find a minimum of both numbers.
-  let less = arg1 > arg2 ? arg2 : arg1
-  // Iterate the number and find the gcd of the number using the above explanation.
-  for (less; less >= 2; less--) {
-    if ((arg1 % less === 0) && (arg2 % less === 0)) return (less)
-  }
-  return (less)
+  return a
 }
-
-export { GetEuclidGCD }