素数筛再优化

#include <iostream>
#include <memory.h>
#include <cmath>
using namespace std;
int main()
{
    long long int n;
    cin>>n;
    long long int a[n+1];
    memset(a,0,sizeof(a)+1);
    long long int m = sqrt(n);
    for(long long int i = 2; i <= m; i++)
    {
        if(!a[i])
        {
            for(long long j = i + i; j <= n; j+=i)
                a[j] = 1;
        }
    }
    for(long long int i = 2; i <= n; i++)
        if(!a[i])
            cout<<i<<"\t";
    return 0;
}

优化依据：