[spojRNG]Random Number Generator

All the first number plus Ri, i.e., changes the interval [0,2Ri], consider the inclusion and exclusion, the receiving dismissed interval [0, + oo) - [ 2Ri, + oo), then [2Ri, + oo) Order $ bi = ai-2Ri $, are equivalent to the range [0, + oo)
is transformed and the number does not exceed the number of programs for the sake of b n positive infinity range, and found that wild guess $ b ^ {n} / n! $, violence can be cumulative

 1 #include<bits/stdc++.h>
 2 using namespace std;
 3 #define ld long double
 4 int t,n,x,y,a[11];
 5 ld ans;
 6 ld calc(int k){
 7     if (k<=0)return 0;
 8     ld ans=1;
 9     for(int i=1;i<=n;i++)ans=ans*k/i;
10     return ans; 
11 }
12 int main(){
13     scanf("%d",&t);
14     while (t--){
15         scanf("%d%d%d",&n,&x,&y);
16         ans=0;
17         for(int i=0;i<n;i++){
18             scanf("%d",&a[i]);
19             x+=a[i];
20             y+=a[i];
21             a[i]=a[i]*2;
22         }
23         for(int i=0;i<(1<<n);i++){
24             int p=1,s=0;
25             for(int j=0;j<n;j++)
26                 if (i&(1<<j)){
27                     p*=-1;
28                     s+=a[j];
29                 }
30             ans+=p*(calc(y-s)-calc(x-s));
31         }
32         for(int i=0;i<n;i++)ans/=a[i];
33         printf("%.9Lf\n",ans);
34     }
35 }

View Code