hdu 4465 Candy 2012 成都现场赛

 1 /**
 2 对于大数的很好的应用，，缩小放大，，保持精度
 3 **/
 4 #include <iostream>
 5 #include <cmath>
 6 #include <algorithm>
 7 #include <cstdio>
 8 using namespace std;
 9 
10 int main()
11 {
12     double n,p;
13     int cnt =1;
14     while(cin>>n>>p){
15         double p1 = log(p+0.0);
16         double p2 = log(1-p+0.0);
17         double s1 = (n+1)*p1;
18         double s2 = (n+1)*p2;
19         double ans =0,c=0;
20         for(int i=0;i<n;i++){
21             ans += (exp(c+s1)+exp(c+s2))*(n-i);
22             c += log(n+1+i+0.0)-log(i+1+0.0);
23             s1 += p2;
24             s2 += p1;
25         }
26         printf("Case %d: %.6lf\n",cnt++,ans);
27     }
28     return 0;
29 }