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Merge pull request #351 from JimmyJoo/master

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Improved SieveOfEratosthenes.js
This commit is contained in:
Rak Laptudirm
2021-05-23 13:29:22 +05:30
committed by GitHub
parent c3bf9d6931 e23d09b4f1
commit 38a5cb297a
1 changed files with 9 additions and 1 deletions
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10
Maths/SieveOfEratosthenes.js
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@ -10,7 +10,15 @@ const sieveOfEratosthenes = (n) => {
const sqrtn = Math.ceil(Math.sqrt(n))
for (let i = 2; i <= sqrtn; i++) {
if (primes[i]) {
for (let j = 2 * i; j <= n; j += i) {
for (let j = i * i; j <= n; j += i) {
/*
Optimization.
Let j start from i * i, not 2 * i, because smaller multiples of i have been marked false.
For example, let i = 4.
We do not have to check from 8(4 * 2) to 12(4 * 3)
because they have been already marked false when i=2 and i=3.
*/
primes[j] = false
}
}