Add LuhnAlgorithm.js and LuhnAlgorithm.test.js

Maths/LuhnAlgorithm.js

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+/**
+ * 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.
+ */
+
+// 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

Maths/test/LuhnAlgorithm.test.js

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+// Import the functions to be tested
+import { validateCred, findInvalidCards, idInvalidCardCompanies } from '../LuhnAlgorithm.js';
+
+// Import credit card numbers to be tested
+import { valid1, valid2, valid4, valid3, valid5, invalid1, invalid2, invalid3, invalid4, invalid5, batch} from '../LuhnAlgorithm.js'
+
+// Test suite for credit card validation
+
+  //Test validateCred function
+    function testValidateCred() {
+        console.log('Running tests for validateCred...');
+
+    // Valid test cases
+        if (![valid1, valid2, valid3, valid4, valid5].every(card => validateCred(card))) {
+            console.error('FAILED: validateCred should return true for all valid cards');
+        }
+        if ([invalid1, invalid2, invalid3, invalid4, invalid5].some(card => validateCred(card))) {
+            console.error('FAILED: validateCred should return false for all invalid cards');
+        } else {
+            console.log('PASSED: Valid card test');
+        };
+
+    // Invalid test cases
+        if (validateCred(invalid1 || invalid2 || invalid3 || invalid4 || invalid5)) {
+            console.error('FAILED: validateCred should return false for invalid cards');
+        } else {
+            console.log('PASSED: Invalid card test');
+        }
+    };
+
+  //Test findInvalidCards function
+    function testFindInvalidCards(batch) {
+        console.log('Running tests for findInvalidCards...');
+        const invalidCards = findInvalidCards(batch);
+
+    // Check if the result only contains invalid cards
+        const allInvalid = invalidCards.every(card => !validateCred(card));
+
+        if (!allInvalid) {
+            console.error('FAILED: findInvalidCards should return only invalid cards');
+        } else {
+            console.log('PASSED: Find invalid cards test');
+        }
+    };
+
+  // Test idInvalidCardCompanies function
+    function testIdInvalidCardCompanies() {
+        console.log('Running tests for idInvalidCardCompanies...');
+        const companies = idInvalidCardCompanies(batch);
+
+        if (!companies.includes('Visa') || !companies.includes('Mastercard') || !companies.includes('Amex') || !companies.includes('Discover')) {
+            console.error('FAILED: idInvalidCardCompanies should include all expected companies');
+        } else if (companies.includes('Unknown')) {
+            console.error('FAILED: idInvalidCardCompanies should not include unrecognized prefixes');
+        } else {
+            console.log('PASSED: Identify invalid card companies test');
+        }
+    };
+
+  //Run all tests
+    function runAllTests() {
+        console.log('Starting test suite...');
+        testValidateCred();
+        testFindInvalidCards(batch);
+        testIdInvalidCardCompanies();
+        console.log('Testing edge cases...');
+        console.assert(findInvalidCards([[]]).length === 0, 'FAILED: findInvalidCards should handle empty arrays');
+        console.log('All tests completed.');
+    };
+
+  // Run the test suite
+    runAllTests();