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Refactor linearPrimeSieve.js

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This commit is contained in:
Sandeep Satheesh 2018-10-01 22:35:42 +05:30
parent 65037f32dd
commit b43738839e
1 changed files with 29 additions and 18 deletions
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47
src/algorithms/math/linear-prime-sieve/linearPrimeSieve.js
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@ -3,22 +3,33 @@
* @return {number[]}
*/
export default function linearPrimeSieve(maxNumber) {
const primes =[];
const leastPrimeFactor = new Array(maxNumber + 1).fill(0); // leastPrimeFactor[i] gives us the least prime factor of 'i'
for(let i=2; i<=maxNumber; i++ ){
if(!leastPrimeFactor[i]){ // leastPrimeFactor[i] = 0 means 'i' itself is its least prime factor, i.e 'i' is prime
leastPrimeFactor[i] = i;
primes.push(i);
}
/*
* start setting leastPrimeFactor[] for numbers 'x', where x = p * i, p is x's least prime factor and p <= leastPrimeFactor[i]
* x = p*i, this representation will be unique for any number, therefore leastPrimeFactor[x] will be set only once.
*/
for(let j=0; j<primes.length && primes[j]*i <=maxNumber && primes[j]<=leastPrimeFactor[i]; j++)
leastPrimeFactor[primes[j]*i] = primes[j];
}
return primes;
const primes = [];
// leastPrimeFactor[i] gives us the least prime factor of 'i'
const leastPrimeFactor = new Array(maxNumber + 1).fill(0);
for (let i = 2; i <= maxNumber; i += 1) {
if (!leastPrimeFactor[i]) {
/* leastPrimeFactor[i] = 0 means 'i' itself is its least prime factor,
* i.e 'i' is prime
*/
leastPrimeFactor[i] = i;
primes.push(i);
}
/*
* start setting leastPrimeFactor[] for numbers 'x', where x = p * i, p is x's
* least prime factor and p <= leastPrimeFactor[i]. x = p*i, this representation will
* be unique for any number, therefore leastPrimeFactor[x] will be
* set only once.
*/
let j = 0;
while (j < primes.length) {
if ((primes[j] * i > maxNumber) || (primes[j] > leastPrimeFactor[i])) { break; }
leastPrimeFactor[primes[j] * i] = primes[j];
j += 1;
}
}
return primes;
}