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Remove factors

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Angelos Chalaris
2020-04-16 11:10:44 +03:00
parent 589e78962a
commit ec38b481eb
2 changed files with 0 additions and 62 deletions
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45
snippets_archive/factors.md
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---
title: factors
tags: math,intermediate
---
Returns the array of factors of the given `num`.
If the second argument is set to `true` returns only the prime factors of `num`.
If `num` is `1` or `0` returns an empty array.
If `num` is less than `0` returns all the factors of `-int` together with their additive inverses.
Use `Array.from()`, `Array.prototype.map()` and `Array.prototype.filter()` to find all the factors of `num`.
If given `num` is negative, use `Array.prototype.reduce()` to add the additive inverses to the array.
Return all results if `primes` is `false`, else determine and return only the prime factors using `isPrime` and `Array.prototype.filter()`.
Omit the second argument, `primes`, to return prime and non-prime factors by default.
**Note**:- _Negative numbers are not considered prime._
```js
const factors = (num, primes = false) => {
const isPrime = num => {
const boundary = Math.floor(Math.sqrt(num));
for (var i = 2; i <= boundary; i++) if (num % i === 0) return false;
return num >= 2;
};
const isNeg = num < 0;
num = isNeg ? -num : num;
let array = Array.from({ length: num - 1 })
.map((val, i) => (num % (i + 2) === 0 ? i + 2 : false))
.filter(val => val);
if (isNeg)
array = array.reduce((acc, val) => {
acc.push(val);
acc.push(-val);
return acc;
}, []);
return primes ? array.filter(isPrime) : array;
};
```
```js
factors(12); // [2,3,4,6,12]
factors(12, true); // [2,3]
factors(-12); // [2, -2, 3, -3, 4, -4, 6, -6, 12, -12]
factors(-12, true); // [2,3]
```

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test/factors.test.js
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const {factors} = require('./_30s.js');
test('factors is a Function', () => {
expect(factors).toBeInstanceOf(Function);
});
test('factors returns the correct array', () => {
expect(factors(12)).toEqual([2, 3, 4, 6, 12]);
});
test('factors returns the correct array of primes', () => {
expect(factors(12, true)).toEqual([2, 3]);
});
test('factors returns the correct array for negatives', () => {
expect(factors(-12)).toEqual([2, -2, 3, -3, 4, -4, 6, -6, 12, -12]);
});
test('factors returns the correct array of primes for negatives', () => {
expect(factors(-12, true)).toEqual([2, 3]);
});