UVA 10200 Prime Time 水

题目链接：https://uva.onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&page=show_problem&problem=1141

题意：判断区间[a,b]的f（i）是否为素数，f（i）=i*i+i+40；

思路：打个表，然后注意精度；

#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define esp 1e-13
const int N=1e4+10,M=1e6+50000,inf=1e9+10,mod=1000000007;
int prime(int n)
{
if(n<=1)
return 0;
if(n==2)
return 1;
if(n%2==0)
return 0;
int k, upperBound=n/2;
for(k=3; k<=upperBound; k+=2)
{
upperBound=n/k;
if(n%k==0)
return 0;
}
return 1;
}
int f(int x)
{
return x*x+41+x;
}
int flag
;
int main()
{
int x,y,i,z,t;
for(i=0;i<=10000;i++)
if(prime(f(i)))
flag[i+1]=flag[i]+1;
else
flag[i+1]=flag[i];
while(~scanf("%d%d",&x,&y))
{
double sum=flag[y+1]-flag[x];
double di=(y-x+1);
double ans=sum/di*100.0+1e-8;
printf("%.2f\n",ans);
}
return 0;
}