diff --git a/Maths/LuhnAlgorithm.js b/Maths/LuhnAlgorithm.js new file mode 100644 index 0000000000..d338190d08 --- /dev/null +++ b/Maths/LuhnAlgorithm.js @@ -0,0 +1,114 @@ +/** + * Luhn algorithm, also known as the “Modulus 10” or “mod 10” algorithm. + * This algorithm is a simple checksum formula used to validate the authenticity of credit card numbers. + * The Luhn algorithm works by doubling every second digit from right to left, adding the resulting digits, and then checking if the total is divisible by 10. + * If it is, the credit card number is considered valid. + * The Luhn algorithm is widely used in credit card verification and is specified in ISO/IEC 7812-1. + * It is not intended to be a cryptographically secure hash function but rather a simple method to detect accidental errors, not malicious attacks. + * https://en.wikipedia.org/wiki/Luhn_algorithm + */ + +// Valid credit card numbers +export const valid1 = [4, 5, 3, 9, 6, 7, 7, 9, 0, 8, 0, 1, 6, 8, 0, 8] +export const valid2 = [5, 5, 3, 5, 7, 6, 6, 7, 6, 8, 7, 5, 1, 4, 3, 9] +export const valid3 = [6, 0, 1, 1, 1, 4, 4, 3, 4, 0, 6, 8, 2, 9, 0, 5] +export const valid4 = [3, 7, 1, 6, 1, 2, 0, 1, 9, 9, 8, 5, 2, 3, 6] +export const valid5 = [4, 5, 3, 9, 4, 0, 4, 9, 6, 7, 8, 6, 9, 6, 6, 6] + +// Invalid credit card numbers +export const invalid1 = [4, 5, 3, 2, 7, 7, 8, 7, 7, 1, 0, 9, 1, 7, 9, 5] +export const invalid2 = [5, 7, 9, 5, 5, 9, 3, 3, 9, 2, 1, 3, 4, 6, 4, 3] +export const invalid3 = [3, 7, 5, 7, 9, 6, 0, 8, 4, 4, 5, 9, 9, 1, 4] +export const invalid4 = [6, 0, 1, 1, 1, 2, 7, 9, 6, 1, 7, 7, 7, 9, 3, 5] +export const invalid5 = [5, 3, 8, 2, 0, 1, 9, 7, 7, 2, 8, 8, 3, 8, 5, 4] + +// Mixed batch of credit card numbers +export const mystery1 = [3, 4, 4, 8, 0, 1, 9, 6, 8, 3, 0, 5, 4, 1, 4] +export const mystery2 = [5, 4, 6, 6, 1, 0, 0, 8, 6, 1, 6, 2, 0, 2, 3, 9] +export const mystery3 = [ + 6, 0, 1, 1, 3, 7, 7, 0, 2, 0, 9, 6, 2, 6, 5, 6, 2, 0, 3 +] +export const mystery4 = [4, 9, 2, 9, 8, 7, 7, 1, 6, 9, 2, 1, 7, 0, 9, 3] +export const mystery5 = [4, 9, 1, 3, 5, 4, 0, 4, 6, 3, 0, 7, 2, 5, 2, 3] + +export const batch = [ + valid1, + valid2, + valid3, + valid4, + valid5, + invalid1, + invalid2, + invalid3, + invalid4, + invalid5, + mystery1, + mystery2, + mystery3, + mystery4, + mystery5 +] + +/** + * Validates a credit card number using the Luhn Algorithm. + * @param {number[]} numArr - Array representing the credit card number. + * @returns {boolean} - True if the card is valid, false otherwise. + */ +export function validateCred(numArr) { + let total = 0 + for (let i = numArr.length - 1; i >= 0; i--) { + let currValue = numArr[i] + // Double every other digit starting from the second-to-last + if ((numArr.length - 1 - i) % 2 === 1) { + currValue *= 2 + if (currValue > 9) { + currValue -= 9 + } + } + total += currValue + } + return total % 10 === 0 +} + +/** + * Finds invalid credit card numbers from a batch. + * @param {number[][]} cards - Array of credit card numbers. + * @returns {number[][]} - Array of invalid credit card numbers. + */ +export function findInvalidCards(cards) { + return cards.filter((card) => !validateCred(card)) +} + +/** + * Identifies credit card companies that issued invalid card numbers. + * @param {number[][]} invalidBatch - Array of invalid credit card numbers. + * @returns {string[]} - Array of company names. + */ +export function idInvalidCardCompanies(invalidBatch) { + const companies = new Set() + invalidBatch.forEach((card) => { + switch (card[0]) { + case 3: + companies.add('Amex') + break + case 4: + companies.add('Visa') + break + case 5: + companies.add('Mastercard') + break + case 6: + companies.add('Discover') + break + default: + console.warn('Company not found for card starting with:', card[0]) + } + }) + return Array.from(companies) +} + +// Example Usage +console.log(validateCred(valid1)) // Should print true +console.log(validateCred(invalid1)) // Should print false +console.log(findInvalidCards(batch)) // Find all invalid cards +console.log(idInvalidCardCompanies(findInvalidCards(batch))) // Find companies of invalid cards diff --git a/Maths/test/LuhnAlgorithm.test.js b/Maths/test/LuhnAlgorithm.test.js new file mode 100644 index 0000000000..e8812a3033 --- /dev/null +++ b/Maths/test/LuhnAlgorithm.test.js @@ -0,0 +1,80 @@ +// Import the functions to be tested +import { + validateCred, + findInvalidCards, + idInvalidCardCompanies +} from '../LuhnAlgorithm.js' +// Import credit card numbers to be tested +import { + valid1, + valid2, + valid3, + valid4, + valid5, + invalid1, + invalid2, + invalid3, + invalid4, + invalid5, + batch +} from '../LuhnAlgorithm.js' + +describe('Luhn Algorithm Tests', () => { + // Test for validateCred function + describe('validateCred', () => { + test('should return true for valid credit cards', () => { + const validCards = [valid1, valid2, valid3, valid4, valid5] + validCards.forEach((card) => { + expect(validateCred(card)).toBe(true) + }) + }) + + test('should return false for invalid credit cards', () => { + const invalidCards = [invalid1, invalid2, invalid3, invalid4, invalid5] + invalidCards.forEach((card) => { + expect(validateCred(card)).toBe(false) + }) + }) + }) + + // Test for findInvalidCards function + describe('findInvalidCards', () => { + test('should return only invalid credit cards from a batch', () => { + const invalidCards = findInvalidCards(batch) + const allInvalid = invalidCards.every((card) => !validateCred(card)) + expect(allInvalid).toBe(true) + }) + + test('should return an empty array if no invalid cards are found', () => { + const validCards = [valid1, valid2, valid3, valid4, valid5] + const invalidCards = findInvalidCards(validCards) + expect(invalidCards).toEqual([]) + }) + }) + + // Test for idInvalidCardCompanies function + describe('idInvalidCardCompanies', () => { + test('should identify all companies that issued invalid cards', () => { + const invalidCards = findInvalidCards(batch) + const companies = idInvalidCardCompanies(invalidCards) + + // Expect the companies array to include known companies + expect(companies).toEqual( + expect.arrayContaining(['Visa', 'Mastercard', 'Amex', 'Discover']) + ) + }) + + test('should return an empty array if no invalid cards are found', () => { + const validCards = [valid1, valid2, valid3, valid4, valid5] + const invalidCards = findInvalidCards(validCards) // Ensure only invalid cards are processed + const companies = idInvalidCardCompanies(invalidCards) + expect(companies).toEqual([]) + }) + + test('should handle unknown card companies gracefully', () => { + const unknownCard = [9, 3, 1, 8, 2, 0, 7, 4, 5, 6, 7, 8, 9] + const companies = idInvalidCardCompanies([unknownCard]) + expect(companies).not.toContain('Unknown') + }) + }) +})