区间筛素数模板

#include 
using namespace std;
typedef long long ll;
const int MAX = 1e5+10;
const int MAX_INTERVAL = 2e5+100;
bool is_prime[MAX_INTERVAL];
bool is_prime_small[MAX];
int segment_sieve(ll a,ll b){
    for(int i = 0; (ll)i * i <= b; i++) is_prime_small[i] = true;
    for(int i = 0; i <= b - a; i++) is_prime[i] = true;

    for(int i = 2; (ll)i * i <= b; i++){
       if(is_prime_small[i]){
          for(int j = 2 * j; (ll)j * j <= b; j += i)
            s_prime_small[j] = false;
          for(ll j = max(2LL,(a+i-1)/i)*i; j <= b; j += i)
            is_prime[j-a] = false;
      //找到a-b范围内第一个i到倍数将其划去，记录到时候仍然记录离散化后的数组位置
       }
    }
    int ans = 0;
    for(int i = 0; i <= b-a; i++){
       if(is_prime[i]) ans++;
    }
    return ans;
}
int main(){
   int T,cas = 0;
   scanf("%d",&T);
   while(T--){
      ll a,b;
      scanf("%lld%lld",&a,&b);
      int ans = segment_sieve(a,b);
      if(a == 1) ans--;
      printf("Case %d: %d\n",++cas,ans);
   }
   return 0;
}