素数筛法

#include <iostream>
using namespace std;
const int MAXN = 65535;
bool prime[MAXN + 1];

int main(){
    for (int i = 0; i <= MAXN; ++i) { //对非偶数标true
        prime[i] = true;
        if (!(i & 1)) {
            prime[i] = false;
        }
    }
    prime[1] = fales; //0和1非素数标fales
    prime[2] = true; //对2标true


    for (int i = 3; i * i <= MAXN; i += 2) {
        if (prime[i]) {
            for (int j = i + i; j <= MAXN; j += i) { //碰见true往后加i，标false
                prime[j] = false;
            }
        }
    }
    return 0;
}