HDU 4336 Card Collector（容斥）

Card Collector

模板题。

代码：

#include <bits/stdc++.h>
using namespace std;

const int max_n=10100;

int n;
double p[max_n],ans;

void dfs(int x, int tot, double sum)//容斥原理dfs(1,0,0.0)
{
if (x==n+1)
{
if (sum==0.0) return;
if (tot&1)
ans+=1/sum;
else
ans-=1/sum;
return;
}
dfs(x+1,tot,sum);
dfs(x+1,tot+1,sum+p[x]);
}

int main()
{
while(cin>>n)
{
for (int i=1; i<=n; i++)
cin>>p[i];
ans=0;
dfs(1,0,0.0);
printf("%.4f\n",ans);
}
return 0;
}