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Resolve duplicate entries for sieve of eratosthenes #1770

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1 change: 0 additions & 1 deletion DIRECTORY.md
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Expand Up @@ -254,7 +254,6 @@
* [RowEchelon](Maths/RowEchelon.js)
* [ShorsAlgorithm](Maths/ShorsAlgorithm.js)
* [SieveOfEratosthenes](Maths/SieveOfEratosthenes.js)
* [SieveOfEratosthenesIntArray](Maths/SieveOfEratosthenesIntArray.js)
* [Signum](Maths/Signum.js)
* [SimpsonIntegration](Maths/SimpsonIntegration.js)
* [Softmax](Maths/Softmax.js)
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43 changes: 22 additions & 21 deletions Maths/SieveOfEratosthenes.js
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@@ -1,25 +1,26 @@
const sieveOfEratosthenes = (n) => {
/*
* Calculates prime numbers till a number n
* :param n: Number up to which to calculate primes
* :return: A boolean list containing only primes
*/
const primes = new Array(n + 1)
primes.fill(true) // set all as true initially
primes[0] = primes[1] = false // Handling case for 0 and 1
const sqrtn = Math.ceil(Math.sqrt(n))
for (let i = 2; i <= sqrtn; i++) {
if (primes[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.
/**
* @function sieveOfEratosthenes
* @description Function to get all the prime numbers below a given number using sieve of eratosthenes algorithm
* @param {Number} max The limit below which all the primes are required to be
* @returns {Number[]} An array of all the prime numbers below max
* @see [Sieve of Eratosthenes](https://en.wikipedia.org/wiki/Sieve_of_Eratosthenes)
* @example
* sieveOfEratosthenes(1) // ====> []
* @example
* sieveOfEratosthenes(20) // ====> [2, 3, 5, 7, 11, 13, 17, 19]
*
*/
function sieveOfEratosthenes(max) {
const sieve = []
const primes = []

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
for (let i = 2; i <= max; ++i) {
if (!sieve[i]) {
// If i has not been marked then it is prime
primes.push(i)
for (let j = i << 1; j <= max; j += i) {
// Mark all multiples of i as non-prime
sieve[j] = true
}
}
}
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24 changes: 0 additions & 24 deletions Maths/SieveOfEratosthenesIntArray.js
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37 changes: 26 additions & 11 deletions Maths/test/SieveOfEratosthenes.test.js
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import { sieveOfEratosthenes } from '../SieveOfEratosthenes'
import { PrimeCheck } from '../PrimeCheck'

describe('should return an array of prime booleans', () => {
it('should have each element in the array as a prime boolean', () => {
const n = 30
const primes = sieveOfEratosthenes(n)
primes.forEach((primeBool, index) => {
if (primeBool) {
expect(PrimeCheck(index)).toBeTruthy()
}
})

describe('sieveOfEratosthenes', () => {
test('returns an empty array for max < 2', () => {
expect(sieveOfEratosthenes(1)).toEqual([])
})

test('returns [2] for max = 2', () => {
expect(sieveOfEratosthenes(2)).toEqual([2])
})

test('returns [2, 3] for max = 3', () => {
expect(sieveOfEratosthenes(3)).toEqual([2, 3])
})

test('returns [2, 3, 5, 7] for max = 10', () => {
expect(sieveOfEratosthenes(10)).toEqual([2, 3, 5, 7])
})

test('returns [2, 3, 5, 7, 11, 13, 17, 19] for max = 20', () => {
expect(sieveOfEratosthenes(20)).toEqual([2, 3, 5, 7, 11, 13, 17, 19])
})

test('returns [2, 3, 5, 7, 11, 13, 17, 19, 23, 29] for max = 30', () => {
expect(sieveOfEratosthenes(30)).toEqual([
2, 3, 5, 7, 11, 13, 17, 19, 23, 29
])
})
})
12 changes: 0 additions & 12 deletions Maths/test/SieveOfEratosthenesIntArray.test.js
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2 changes: 1 addition & 1 deletion Project-Euler/Problem035.js
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Expand Up @@ -9,7 +9,7 @@
*
* @author ddaniel27
*/
import { sieveOfEratosthenes } from '../Maths/SieveOfEratosthenesIntArray'
import { sieveOfEratosthenes } from '../Maths/SieveOfEratosthenes'

function problem35(n) {
if (n < 2) {
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