Leetcode Problem 493. Reverse Pairs

493. Reverse Pairs

Leetcode Solutions

Define a recursive function mergeSort that takes the array nums and the indices left and right as arguments.
If left is greater than or equal to right, return 0 as there are no reverse pairs to count.
Calculate the middle index mid as (left + right) / 2.
Recursively call mergeSort on the left subarray (left to mid) and the right subarray (mid + 1 to right) and sum their returned reverse pair counts.
Initialize two pointers, i to left and j to mid + 1.
For each element in the left subarray, count the elements in the right subarray that form a reverse pair with it and add this count to the total reverse pair count.
Merge the two sorted subarrays while maintaining their sorted order.
Return the total reverse pair count.

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