An inversion in a sequence A[1..n] is defined as i, j, 1 ≤ i < j ≤ n, such that A[i] > A[j]. For example, the sequence A = {1, 5, 2, 4, 3} contains 4 inversions, from the pairs (5, 2), (5, 4), (5, 3), (4, 3).
Your task is simple: Given a sequence, determine the number of inversions in the sequence.
The first line of input will be an integer T (T ≤ 100), stating the number of test cases.
T test cases follow, each in the following format:
First line: An integer N (N ≤ 50,000),
Next line: N integers, giving the values of A[1], A[2], ..., A[N]. You may assume that 0 ≤ A[k] ≤ 2,147,483,647 for all k ≤ N.
3 5 1 5 2 4 3 5 1 2 3 4 5 6 6 5 4 3 2 1
4 0 15
Subtask | Score |
---|---|
1 | 100 |
2 | 0 |