注意精度。
/* *********************************************** Author : ryc Created Time : 2016-08-14 Sunday File Name : E:\acm\大三暑假\uva10200.cpp Language : c++ Copyright 2016 ryc All Rights Reserved ************************************************ */ #include<iostream> #include<cstdio> #include<cstdlib> #include<algorithm> #include<cstring> #include<queue> #include<list> #include<stack> #include<vector> #include<map> using namespace std; typedef long long LL; typedef pair<int,int>pii; const int maxn=10010; double ans[maxn]; bool judge(LL n){ for(LL i=2;i*i<=n;++i){ if(n%i==0)return false; } return true; } void Count(){ ans[0]=1; for(LL i=1;i<maxn;++i){ if(judge(i*i+i+41)){ ans[i]=ans[i-1]+1; } else { ans[i]=ans[i-1]; } } } int main() { Count(); int a,b; while(scanf("%d%d",&a,&b)!=EOF){ if(a==0){ printf("%.2lf\n",ans[b]*1.0/(b+1)*100.0+1e-8); } else { printf("%.2lf\n",(double)(1.0*(ans[b]-ans[a-1])*1.0/(b-a+1))*100.0+1e-8); } } return 0; }
