素数打表

void init_prim()
{
    memset(visit, true, sizeof(visit));
    int num = 0;
    for (int i = 2; i <= 1000000; ++i)
    {
        if (visit[i] == true)
        {
            num++;
            prime[num] = i;
            //mp[i]=num;
        }
        for (int j = 1; ((j <= num) && (i * prime[j] <= 1000000));  ++j)
        {
            visit[i * prime[j]] = false;
            if (i % prime[j] == 0) break; //点睛之笔
        }
    }
}

void init_prim()
{
    memset(visit, true, sizeof(visit));
    int num = 0;
    for (int i = 2; i <= 1000000; ++i)
    {
        for(int j=i+i;j<=1000000;j=j+i)
            visit[j]=false;
    }
    for(int i=2;i<=1000000;i++)
        if(visit[i])
    {
        prime[++num]=i;
        //mp[i]=num;
    }
}