Sieve of Eratosthenes

primes.cpp

#include <vector>
#include <cmath>
using namespace std;

vector<int> primes(int n)
{
	vector<bool> table(n + 1, true);
	table[0] = table[1] = false;
	int mid = (int)floor(sqrt(n));
	for (int i = 2; i <= mid; i++) {
		if (table[i]) {
			for (int j = i+i; j <= n; j += i)
				table[j] = false;
		}
	}
	vector<int> ans;
	for (int i = 2; i <= n; i++)
		if (table[i])
			ans.push_back(i);
	return ans;
}