36 lines
1.1 KiB
Markdown
36 lines
1.1 KiB
Markdown
---
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title: luhnCheck
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tags: math,algorithm,advanced
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firstSeen: 2018-01-03T11:02:35+02:00
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lastUpdated: 2020-12-28T13:49:24+02:00
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---
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Implementation of the [Luhn Algorithm](https://en.wikipedia.org/wiki/Luhn_algorithm) used to validate a variety of identification numbers, such as credit card numbers, IMEI numbers, National Provider Identifier numbers etc.
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- Use `String.prototype.split('')`, `Array.prototype.reverse()` and `Array.prototype.map()` in combination with `parseInt()` to obtain an array of digits.
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- Use `Array.prototype.splice(0, 1)` to obtain the last digit.
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- Use `Array.prototype.reduce()` to implement the Luhn Algorithm.
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- Return `true` if `sum` is divisible by `10`, `false` otherwise.
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```js
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const luhnCheck = num => {
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let arr = (num + '')
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.split('')
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.reverse()
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.map(x => parseInt(x));
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let lastDigit = arr.splice(0, 1)[0];
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let sum = arr.reduce(
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(acc, val, i) => (i % 2 !== 0 ? acc + val : acc + ((val *= 2) > 9 ? val - 9 : val)),
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0
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);
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sum += lastDigit;
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return sum % 10 === 0;
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};
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```
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```js
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luhnCheck('4485275742308327'); // true
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luhnCheck(6011329933655299); // true
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luhnCheck(123456789); // false
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```
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