Leetcode Problem 493. Reverse Pairs

493. Reverse Pairs

Leetcode Solutions

Merge Sort Approach for Counting Reverse Pairs

  1. Define a recursive function mergeSort that takes the array nums and the indices left and right as arguments.
  2. If left is greater than or equal to right, return 0 as there are no reverse pairs to count.
  3. Calculate the middle index mid as (left + right) / 2.
  4. 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.
  5. Initialize two pointers, i to left and j to mid + 1.
  6. 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.
  7. Merge the two sorted subarrays while maintaining their sorted order.
  8. Return the total reverse pair count.
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Brute Force Approach for Counting Reverse Pairs

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