Eratosthenes Seive

计算\(\pi(x)和打质数表\)
code:

#include<cstdio>
#include<vector>
using std::vector;
int seive(vector<int>& prime, const int& x) {
	bool* A = new bool[x + 1];
	for (int i = 2; i <= x; i++)A[i] = 1;
	for (int p = 2; p * p <= x; p++)if (A[p])for (int i = p * p; i <= x; i += p)A[i] = 0;
	int pi = 0;
	for (int i = 2; i <= x; i++) if(A[i]){
		prime.push_back(i);
		++pi;
	}
	delete[] A;
	return pi;
}
int main() {
	int x;
	vector<int>prime;
	scanf("%d", &x);
	printf("%d\n", seive(prime, x));
	for (auto& p : prime)printf("%d ", p);
}