INVCNT  Inversion Count
Let A[0...n  1] be an array of n distinct positive integers. If i < j and A[i] > A[j] then the pair (i, j) is called an inversion of A. Given n and an array A your task is to find the number of inversions of A.
Input
The first line contains t, the number of testcases followed by a blank space. Each of the t tests start with a number n (n <= 200000). Then n + 1 lines follow. In the ith line a number A[i  1] is given (A[i  1] <= 10^7). The (n + 1)th line is a blank space.
Output
For every test output one line giving the number of inversions of A.
Example
Input: 2 3 3 1 2 5 2 3 8 6 1 Output: 2 5
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pirate_joker1:
20190815 12:14:19
solved it using PBDS 

bogdanvlad:
20190709 00:47:06
AC in one go using merge sort, very nice problem 

howdy_1999:
20190708 16:00:46
Divide and conquer approach 

sajalagrawal14:
20190701 16:11:36
good problem.


killerjay:
20190625 19:18:46
just store the element and index in pair and after that sort pair in decreasing order with respect to first element


smrtdvlpr:
20190625 12:26:45
Great problem, can be done easily using divide and conquer.


rohan_24:
20190528 10:17:07
can anyone tell,how to solve this by BIT?


hetp111:
20190527 08:33:53
Great problem...! can be done using D&C, BIT or Segment Tree... 

walter_whitee:
20190424 00:27:33
AC in one go using divide and conquer technique :D 

gabrijel:
20190327 23:41:09
Yes, output can be up to n^2 so O(n^2) should definitely pass. 
Added by:  Paranoid Android 
Date:  20100306 
Time limit:  3.599s 
Source limit:  50000B 
Memory limit:  1536MB 
Cluster:  Cube (Intel G860) 
Languages:  All except: PERL6 