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92 lines
1.7 KiB
Markdown
92 lines
1.7 KiB
Markdown
---
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id: 6a0dcd03ee4e68698080ef6c
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title: "Challenge 308: Credit Card Validator"
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challengeType: 28
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dashedName: challenge-308
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---
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# --description--
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Given a string of digits for a credit card number, determine if it's a valid card number using the following method:
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- Starting from the second-to-last digit, double every other digit moving left.
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- If doubling a digit results in a number greater than 9, subtract 9.
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- Sum all the digits (doubled and undoubled).
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- If the total is divisible by 10, the number is valid.
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# --hints--
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`isValidCard("4532015112830366")` should return `true`.
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```js
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assert.isTrue(isValidCard("4532015112830366"));
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```
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`isValidCard("5425233430109903")` should return `true`.
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```js
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assert.isTrue(isValidCard("5425233430109903"));
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```
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`isValidCard("371449635398431")` should return `true`.
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```js
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assert.isTrue(isValidCard("371449635398431"));
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```
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`isValidCard("6011111111111117")` should return `true`.
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```js
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assert.isTrue(isValidCard("6011111111111117"));
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```
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`isValidCard("4532015112830367")` should return `false`.
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```js
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assert.isFalse(isValidCard("4532015112830367"));
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```
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`isValidCard("1234567890123456")` should return `false`.
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```js
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assert.isFalse(isValidCard("1234567890123456"));
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```
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`isValidCard("4532015112830368")` should return `false`.
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```js
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assert.isFalse(isValidCard("4532015112830368"));
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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 isValidCard(number) {
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return number;
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}
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```
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# --solutions--
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```js
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function isValidCard(number) {
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let sum = 0;
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for (let i = number.length - 1; i >= 0; i--) {
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let digit = parseInt(number[i]);
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if ((number.length - 1 - i) % 2 === 1) {
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digit *= 2;
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if (digit > 9) digit -= 9;
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}
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sum += digit;
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}
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return sum % 10 === 0;
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}
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```
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