soj#532 set p3175

传送门

分析

代码

#include<bits/stdc++.h>
using namespace std;
const double eps = 1e-;
double p[<<],Ans;
int n,m,N;
inline int sum(int x){
    int res=;
    while(x){
      if(x&)res++;
      x>>=;
    }
    return res;
}
int main(){
    int i,j,k;
    scanf("%d",&n);
    N=<<n;
    for(i=;i<N;i++)scanf("%lf",&p[i]);
    for(i=;i<N;i<<=)
      for(j=;j<N;j+=(i<<))
        for(k=;k<i;k++)
          p[i+j+k]+=p[j+k];
    for(i=;i<N;i++)if(-p[(N-)^i]>eps)
      Ans+=((sum(i)&)?:-)/(-p[(N-)^i]);
    if(Ans<1e-)puts("INF");
      else printf("%0.6lf\n",Ans);
    return ;
}