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
gabrijel:
20190327 23:41:09
Yes, output can be up to n^2 so O(n^2) should definitely pass. 

fabijanb:
20190327 21:50:29
original problem, I know how to solve it, is O(n ^ 2) okay? 

linkret:
20190327 16:12:41
not bad task... 

kcluez:
20190323 12:00:43
use long long to store the count of inversions because the number of inversions in the worst case can be n^2 when the array is reverse sorted.Got 2 WA due to this mistake. finally solved. 

ab_biswas09:
20190307 13:47:32
SOLVED using BIT in one go 

masterchef2209:
20190306 15:55:46
solved this problem after months. really good question 

dkkv0000:
20190120 19:49:52
@marethyu thank u 

iamjacksparrow:
20190118 23:37:10
used bit to solve 

striver_79:
20190117 09:09:39
Try solving https://codeforces.com/problemset/problem/459/D after you solve this. 

marethyu1:
20190101 20:58:36
Use long long when counting inversions, it cost me several WAs! 
Added by:  Paranoid Android 
Date:  20100306 
Time limit:  3.599s 
Source limit:  50000B 
Memory limit:  1536MB 
Cluster:  Cube (Intel G860) 
Languages:  All except: PERL6 