4
9
1 1 1 1 1 0 0 1 1
9
1 1 0 0 1 1 1 1 1
4
0 0 1 1
4
0 1 1 1

1.428571
1.000000
0.000000
0.000000

#include <cstdio>
#include <cstring>
#include <stack>
using namespace std;
int const MAX = 1e5 + 5;

struct DIVIDE
{
    int c0, c1;
    double val;
}d[MAX];

int a[MAX];
stack <DIVIDE> stk;

int main()
{
    int T, n;
    scanf("%d", &T);
    while(T--)
    {
        double ans = 0;
        memset(a, 0, sizeof(a));
        scanf("%d", &n);
        int st = 1, ed = n;
        for(int i = 1; i <= n; i++)
            scanf("%d", &a[i]);
        while(ed >= 1 && a[ed] == 1)
            ed --;
        while(st <= n && a[st] == 0)
            st ++;
        int cnt = 0;
        for(int i = st; i <= ed; i++)
        {
            if(a[i] == 1)
            {
                if(a[i - 1] == 0)
                {
                    cnt ++;
                    d[cnt].c0 = d[cnt].c1 = 0;
                }
                d[cnt].c1 ++;
            }
            else
                d[cnt].c0 ++;
        }
        for(int i = 1; i <= cnt; i++)
            d[i].val = (d[i].c1 * 1.0) / ((d[i].c1 + d[i].c0) * 1.0);
        for(int i = 1; i <= cnt; i++)
        {
            if(stk.empty() || d[i].val >= stk.top().val)
                stk.push(d[i]);
            else
            {
                while(!stk.empty() && d[i].val < stk.top().val)
                {
                    d[i].c0 += stk.top().c0;
                    d[i].c1 += stk.top().c1;
                    d[i].val = (d[i].c1 * 1.0) / ((d[i].c1 + d[i].c0) * 1.0);
                    stk.pop();
                }
                i --;
            }
        }
        while(!stk.empty())
        {
            int c1 = stk.top().c1;
            int c0 = stk.top().c0;
            double val = stk.top().val;
            ans += c1 * (1.0 - val) * (1.0 - val) + c0 * val * val;
            stk.pop();
        }
        printf("%.6f\n", ans);
    }
}