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] ≤ 107). 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
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scorpion_ajay:
2017-01-19 11:44:24
best for learners, learning overloaded, spent two days, came out of no hope.
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gauravgb21:
2016-12-29 07:59:30
jst modify the mergesort algorithm
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aditya930:
2016-12-27 23:53:59
use enhanced merge sort and long long to get AC !! |
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supercool2204:
2016-12-27 20:40:05
Last edit: 2017-06-02 15:15:34 |
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aditya9125:
2016-12-25 21:12:12
Use long long for no_of_inversions as max no of inversions could occur in the case when list has all the elements in strictly decreasing order ,i.e max_inversions=n(n-1)/2; |
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vstepano:
2016-12-15 19:36:07
I managed to solve this problem with 2 different programs. One using Merge Sort and one using the BIT (Binary Indexed Tree Peter M. Fenwick). My implementation that used Merge sort had a lot more code than the BIT one, but in the end the Merge sort solution was faster. |
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sergio471:
2016-12-08 21:39:57
too many WA because size_t is not necessarily unsigned long long |
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mohitgupta07:
2016-12-02 12:13:39
Got my error..did my code in eclipse..and just copy pasted it..forgot to remove my package line in the code...costed my NZEC :P :P :P |
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mohitgupta07:
2016-12-02 12:03:39
Simple .. BitMasking.. I mean Fenwick rocks :) :) Simple concept and simple logic.. Also can anyone explain why java gave NZEC for the same code in c++. Also take great care of choosing your data type. costed me 3 WA's . Nice ques and a good way to understand Fenwick :) . |
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rohan_12_11:
2016-11-16 10:34:27
use long long to get AC. Use ORDER STATISTIC BST algorithm.
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| Added by: | Paranoid Android |
| Date: | 2010-03-06 |
| Time limit: | 3.599s |
| Source limit: | 50000B |
| Memory limit: | 1536MB |
| Cluster: | Cube (Intel G860) |
| Languages: | All except: PERL6 |
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