26 lines
746 B
Markdown
26 lines
746 B
Markdown
---
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title: primes
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tags: math,algorithm,intermediate
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firstSeen: 2017-12-21T12:20:22+02:00
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lastUpdated: 2020-12-28T13:49:24+02:00
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---
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Generates primes up to a given number, using the Sieve of Eratosthenes.
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- Generate an array from `2` to the given number.
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- Use `Array.prototype.filter()` to filter out the values divisible by any number from `2` to the square root of the provided number.
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```js
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const primes = num => {
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let arr = Array.from({ length: num - 1 }).map((x, i) => i + 2),
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sqroot = Math.floor(Math.sqrt(num)),
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numsTillSqroot = Array.from({ length: sqroot - 1 }).map((x, i) => i + 2);
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numsTillSqroot.forEach(x => (arr = arr.filter(y => y % x !== 0 || y === x)));
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return arr;
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};
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```
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```js
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primes(10); // [2, 3, 5, 7]
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```
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