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;
}
}