Create Q13-Count Inversions

Amazon/Q13-Count Inversions

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+Given an array of integers. Find the Inversion Count in the array. 
+
+Inversion Count: For an array, inversion count indicates how far (or close) 
+the array is from being sorted. If the array is already sorted 
+then the inversion count is 0.
+If an array is sorted in the reverse order then the inversion count is the maximum. 
+
+Formally, two elements a[i] and a[j] form an inversion if a[i] > a[j] and i < j.
+
+Example 1:
+Input: N = 5, arr[] = {2, 4, 1, 3, 5}
+Output: 3
+Explanation: The sequence 2, 4, 1, 3, 5 
+has three inversions (2, 1), (4, 1), (4, 3).
+
+Example 2:
+Input: N = 5
+arr[] = {2, 3, 4, 5, 6}
+Output: 0
+Explanation: As the sequence is already 
+sorted so there is no inversion count.
+
+Example 3:
+Input: N = 3, arr[] = {10, 10, 10}
+Output: 0
+Explanation: As all the elements of array 
+are same, so there is no inversion count.
+
+Expected Time Complexity: O(NLogN).
+Expected Auxiliary Space: O(N).
+
+Constraints:
+1 ≤ N ≤ 5*105
+1 ≤ arr[i] ≤ 1018