DZY Loves Balls

Time Limit: 4000/2000 MS (Java/Others) Memory Limit: 262144/262144 K (Java/Others)
Total Submission(s): 661 Accepted Submission(s): 389

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

ai , denoting the numbers on the balls.

(

1≤t≤300,2≤n≤300,1≤ai≤300 )

Output

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

Sample Input

231 2 33100 100 100

Sample Output

0.5000000.000000  
    
    
    
    
    
     
   /*思路：对求号码进行排序 取两次球第一次不放回，所有可能的情况为n*(n-1)，对于每一个球，枚举比他大的球的位置j，n-j即为比第一次球大的数目a，a/(n*(n-1))，即为每一次的概率，累加即为结果 */#include 
    
     #include 
     
      #include 
      
       using namespace std;const int N=300+5;int a[N];int main(){	int t,i,j,n;	double re;	cin>>t;	while(t--){		cin>>n;		re=0;		for(i=0;i
       
        >a[i];		sort(a,a+n);		 for(i=0;i