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     The following title single from https://www.cnblogs.com/Morning-Glory/p/11228082.html orzorzorz

    

SP1026 FAVDICE - Favorite Dice

N a die face, enables seeking desired throw times are thrown into each side.

Relatively routine questions 

I throw now set to face one surface of the new roll a probability (ni) / n.

No side throw new probability i / n.

Therefore, the formula is f [i] = i / nf [i] + (ni) / nf [i + 1] +1 (to roll a)

Simplification is f [i] = f [i + 1] + n / (ni)

 Note that the case of n == 1, 1 / c ++ 0 in case the value is not yet clear.

As direct the f [0] is set to 1 output.

In fact, the formula is very easy to push, but not too long push very unskilled)

 1 #include<bits/stdc++.h>
 2 #define re register int
 3 #define db double
 4 #define maxn 1000+5
 5 using namespace std;
 6 db f[maxn];
 7 int t,n;
 8 int main()
 9 {
10     cin>>t;
11     while(t--)
12     {
13         cin>>n;
14         if(n==1) f[0]=1;
15         else{
16             f[n]=0;
17             for(re i=n-1;i>=0;i--)
18             f[i]=f[i+1]+(db)n/(db)(n-i);
19         }
20         printf("%.2lf",f[0]);
21             cout<<endl;
22     }
23     return 0;
24 }

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