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[N]; 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; }