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
hide comments
amish3:
20210630 06:33:50
Getting TLE, even after using merge sort algorithm and scanf/printf. Any idea. Why it is so 

jasperj1:
20210623 16:15:35
Can be easily solved using the Merge Sort function. Just add some checks while merging and you are good to go. 

loser_404:
20210604 10:02:16
Similar problems using Ordered_set:


vishal55:
20210515 10:21:11
A good problem to learn PBDS if you use C++


dvjpy786:
20210409 10:29:22
Ac in one go using segment tree 

s_sarvesh_18:
20210331 07:07:42
modified merge sort on passing by reference and using printf/scanf (instead of cin/cout ) gets accepted.


rahulreddevil:
20210329 14:22:52
Solved using Fenwick Tree ! 

khoaph:
20210316 08:18:55
Finally get AC by using binary search tree 

yasser1110:
20210224 12:25:00
Return type long long vs int tripped me up. Last edit: 20210224 12:25:12 

goku123456:
20210203 19:32:52
A really good sum. But wasted so much time in tle. Pass by reference to remove tle. 
Added by:  Paranoid Android 
Date:  20100306 
Time limit:  3.599s 
Source limit:  50000B 
Memory limit:  1536MB 
Cluster:  Cube (Intel G860) 
Languages:  All except: PERL6 