126 lines
3.0 KiB
Markdown
126 lines
3.0 KiB
Markdown
---
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id: 5ea28156e79528a9ab248f27
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title: Luhn test of credit card numbers
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challengeType: 1
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forumTopicId: 385284
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dashedName: luhn-test-of-credit-card-numbers
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---
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# --description--
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The Luhn test is used by some credit card companies to distinguish valid credit card numbers from what could be a random selection of digits.
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Those companies using credit card numbers that can be validated by the Luhn test have numbers that pass the following test:
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<ol>
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<li> Reverse the order of the digits in the number.</li>
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<li> Take the first, third, ... and every other odd digit in the reversed digits and sum them to form the partial sum s1</li>
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<li> Taking the second, fourth ... and every other even digit in the reversed digits:</li>
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<ol>
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<li>Multiply each digit by two and sum the digits if the answer is greater than nine to form partial sums for the even digits.</li>
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<li>Sum the partial sums of the even digits to form s2.</li>
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</ol>
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<li>If s1 + s2 ends in zero then the original number is in the form of a valid credit card number as verified by the Luhn test.</li>
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</ol>
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For example, if the trial number is 49927398716:
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```bash
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Reverse the digits:
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61789372994
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Sum the odd digits:
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6 + 7 + 9 + 7 + 9 + 4 = 42 = s1
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The even digits:
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1, 8, 3, 2, 9
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Two times each even digit:
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2, 16, 6, 4, 18
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Sum the digits of each multiplication:
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2, 7, 6, 4, 9
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Sum the last:
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2 + 7 + 6 + 4 + 9 = 28 = s2
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s1 + s2 = 70 which ends in zero which means that 49927398716 passes the Luhn test.
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```
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# --instructions--
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Write a function that will validate a number with the Luhn test. Return true if it's a valid number. Otherwise, return false.
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# --hints--
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`luhnTest` should be a function.
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```js
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assert(typeof luhnTest === 'function');
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```
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`luhnTest("4111111111111111")` should return a boolean.
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```js
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assert(typeof luhnTest('4111111111111111') === 'boolean');
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```
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`luhnTest("4111111111111111")` should return `true`.
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```js
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assert.equal(luhnTest('4111111111111111'), true);
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```
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`luhnTest("4111111111111112")` should return `false`.
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```js
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assert.equal(luhnTest('4111111111111112'), false);
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```
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`luhnTest("49927398716")` should return `true`.
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```js
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assert.equal(luhnTest('49927398716'), true);
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```
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`luhnTest("49927398717")` should return `false`.
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```js
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assert.equal(luhnTest('49927398717'), false);
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```
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`luhnTest("1234567812345678")` should return `false`.
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```js
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assert.equal(luhnTest('1234567812345678'), false);
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```
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`luhnTest("1234567812345670")` should return `true`.
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```js
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assert.equal(luhnTest('1234567812345670'), true);
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```
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# --seed--
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## --seed-contents--
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```js
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function luhnTest(str) {
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}
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```
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# --solutions--
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```js
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function luhnTest(str) {
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var luhnArr = [0, 2, 4, 6, 8, 1, 3, 5, 7, 9];
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var counter = 0;
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var incNum;
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var odd = false;
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var temp = String(str).replace(/[^\d]/g, '');
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if (temp.length == 0) return false;
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for (var i = temp.length - 1; i >= 0; --i) {
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incNum = parseInt(temp.charAt(i), 10);
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counter += (odd = !odd) ? incNum : luhnArr[incNum];
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}
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return counter % 10 == 0;
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}
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```
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