LightOJ - 1197（大整数素数塞）记住

https://vjudge.net/contest/276155#problem/M

#include<cstdio>
#include<cmath>
#include<algorithm>
#include<cstring>
#include<iostream>
using namespace std;
typedef long long ll;
const int N=1e6+5;
int tot=0,ans[N/10];
bool vis[N],v[N];
 
void primer()
{
    memset(vis,true,sizeof(vis));
    for(int i=2;i<N;++i)
    {
        if(vis[i]) ans[++tot]=i;
            for(int j=1;(j<=tot)&&(i*ans[j]<N);++j)
        {
            vis[i*ans[j]]=false;
            if(i%ans[j]==0) break;
        }
    }
}
 
int main()
{
    primer();
    //for(int i = 1;i<=10;++i)
    //cout<<ans[i]<<endl;
    int t,a,b,cas=1;
    scanf("%d",&t);
    while(t--)
    {
        int bns=0,max,min;
        scanf("%d%d",&a,&b);
        if(b<N)
        {
            min=lower_bound(ans+1,ans+tot+1,a)-ans;
            max=upper_bound(ans+1,ans+tot+1,b)-ans;
            bns=max-min;
        }
        else{
                memset(v,true,sizeof(v));
            for(int i=1;(i<=tot)&&(ans[i]<a);++i)
            {
                ll k=a/ans[i];
                if(a%ans[i])  k++;
                for(ll j=k*ans[i];j<=b;j+=ans[i])
                    v[j-a]=false;
            }
            for(int k=0;k<=b-a;++k)
                if(v[k]) bns++;
        }
        printf("Case %d: %d\n",cas++,bns);
    }
}