Prime Genaration

//In the name of ALLAH

#include<bits/stdc++.h>
using namespace std;

#define optimize() ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
#define endl '\n'

const int mx = 1e6+123;

bool is_prime[mx];
vector<int> prime;

void primegen ( int n )
{
    for ( int i = 3; i <= n; i += 2 ) is_prime[i] = 1;

    int sq = sqrt ( n );
    for ( int i = 3; i <= sq; i += 2 ) {
        if ( is_prime[i] == 1 ) {
            for ( int j = i*i; j <= n; j += ( i + i ) ) {
                is_prime[j] = 0;
            }
        }
    }

is_prime[2]=0;
prime.push_back(2);

    for ( int i = 3; i <= n; i += 2 ) {
        if ( is_prime[i] == 1 ) prime.push_back ( i );
    }
}

int main()
{

    //Prime Generation: complexity 0(n) almost
    primegen(100);

    for(auto u: prime)cout << u << " ";
    cout << endl;//2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 89 97


    return 0;
}