#include <bits/stdc++.h>
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;
}
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转载自blog.csdn.net/codeswarrior/article/details/81051736
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