Prime Number
// 특정 숫자가 소수인지 판별하는데 유리 :: O(√n)
function isPrime(num) {
for (let i = 2; i * i <= num; i++) {
if (num % i === 0) return false;
}
return true;
}
// 에라토스테네스의 체. 특정 수까지의 소수를 알아내는데에 유리 O(nlogn)
function getPrimes(num) {
const prime = [false, false, ...Array(num - 1).fill(true)];
for (let i = 2; i * i <= num; i++) {
if (prime[i]) {
for (let j = i * 2; j <= num; j += i) {
prime[j] = false;
}
}
}
return prime;
}
getPrimes(13)
isPrime(13)
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