DZY Loves Balls

DZY Loves Balls

Accepts: 662

Submissions: 1392

Time Limit: 4000/2000 MS (Java/Others)

Memory Limit: 262144/262144 K (Java/Others)

Problem Description

DZY loves playing balls.

He has $n$ balls in a big box. On each ball there is an integer written.

One day he decides to pick two balls from the box. First he randomly picks a ball from the box, and names it $A$. Next, without putting $A$ back into the box, he randomly picks another ball from the box

, and names it $B$.

If the number written on $A$ is strictly greater than the number on $B$, he will feel happy.

Now you are given the numbers on each ball. Please calculate the probability that he feels happy.

Input

First line contains $t$ denoting the number of testcases.

$t$ testcases follow. In each testcase, first line contains $n$, second line contains $n$ space-separated positive integers aia_ia​i​​, denoting the numbers on the balls.

(1≤t≤300,2≤n≤300,1≤ai≤3001\le t\le 300, 2\le n \le 300,1\le a_i \le 3001≤t≤300,2≤n≤300,1≤a​i​​≤300)

Output

For each testcase, output a real number with 6 decimal places.

Sample Input

Copy

2
3
1 2 3
3
100 100 100

Sample Output

Copy

0.500000
0.000000

#include<stdio.h>
#include<algorithm>
using namespace std;
int a[1000];
int main()
{
    int t,n,i,j;
    double b;
    scanf("%d",&t);
    while(t--)
    {
        scanf("%d",&n);
        for(i=0;i<n;i++)
        {
            scanf("%d",&a[i]);
        }
        double p;
        p=n*(n-1);
        sort(a,a+n);
        double sum=0;
        for(i=n-1;i>=0;i--)
        {
            for(j=i-1;j>=0;j--)
            {
                if(a[i]>a[j])
                {
                    sum=sum+1;
                }
            }
        }
      b=sum/p;
      printf("%.6lf\n",b);
    }
}