BUAACM 晴天小猪是点赞狂魔

简单题，并且数据还有问题！

#include <iostream>#include <cstring>#include <iomanip>using namespace std;int main(){int T;long long i, n;cin>>T;while (T--){cin>>n;long long a;long long t = (n+1) * n / 2;long long k = 0;for (i = 1; i <= n; ++i){cin>>a;k += a * i*(n-i+1);}cout<<setiosflags(ios::fixed)<<setprecision(3)<<(double)k/t<<endl;}return 0;}