UVA 10900 So you want to be a 2n-aire?

参考

http://www.cnblogs.com/staginner/archive/2011/12/13/2286691.html

#include <map>
#include <set>
#include <list>
#include <cmath>
#include <ctime>
#include <deque>
#include <stack>
#include <queue>
#include <cctype>
#include <cstdio>
#include <string>
#include <vector>
#include <climits>
#include <cstdlib>
#include <cstring>
#include <iostream>
#include <algorithm>
#define LL long long
#define PI 3.1415926535897932626
using namespace std;
int gcd(int a, int b) {return a % b == 0 ? b : gcd(b, a % b);}
#define MAXN 35
double v[MAXN],ans,T;
int N;
int main()
{
    v[0]=1;
    for (int i=1;i<=30;i++) v[i]=v[i-1]*2;
    while (scanf("%d%lf",&N,&T)!=EOF)
    {
        if (N==0 && T==0) break;
        if (fabs(1-T)<1e-9) {printf("%.3lf
",v[N]);continue;}
        double ans=v[N];
        for (int i=N-1;i>=0;i--)
        {
            double f=v[i]/ans;
            if (f<=T)  ans=(1+T)/2*ans;
            else ans=(f-T)/(1-T)*v[i]+(1-f)/(1-T)*(1+f)/2*ans;
        }
        printf("%.3lf
",ans);
    }
    return 0;
}