lightoj1197区间素数筛

Posted 2020-09-29 walfy

模板题，不过好像有点问题，当a==1的时候，答案把一也算进去了，要减去

#include<map>
#include<set>
#include<cmath>
#include<queue>
#include<stack>
#include<vector>
#include<cstdio>
#include<cassert>
#include<iomanip>
#include<cstdlib>
#include<cstring>
#include<iostream>
#include<algorithm>
#define pi acos(-1.0)
#define ll long long
#define mod 1000000007
#define ls l,m,rt<<1
#define rs m+1,r,rt<<1|1
#pragma comment(linker, "/STACK:1024000000,1024000000")

using namespace std;

const double g=10.0,eps=1e-7;
const int N=100000+10,maxn=500+100,inf=0x3f3f3f;

bool prime[N],primesmall[N];
ll seg_prime(ll a,ll b)
{
    memset(prime,0,sizeof prime);
    for(ll i=0;i*i<b;i++)primesmall[i]=1;
    for(ll i=0;i<=b-a;i++)prime[i]=1;
    for(ll i=2;i*i<b;i++)
    {
        if(primesmall[i])
        {
            for(ll j=2*i;j*j<b;j+=i)primesmall[j]=0;
            for(ll j=max((ll)2,(a+i-1)/i)*i;j<=b;j+=i)prime[j-a]=0;
        }
    }
    ll ans=0;
    for(ll i=0;i<=b-a;i++)
        if(prime[i])
           ans++;
    return ans;
}
int main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);
    ll t,cnt=0;
    cin>>t;
    while(t--){
        ll a,b;
        cin>>a>>b;
        if(a==1)cout<<"Case "<<++cnt<<": "<<seg_prime(a,b)-1<<endl;
        else cout<<"Case "<<++cnt<<": "<<seg_prime(a,b)<<endl;
    }
    return 0;
}
/*********************
9
2 36
3 73
3 11
1 1
1 2
2147383647 2147483647
23990500 24000500
24000501 24100501
23999500 24010501
*********************/

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