Count Inversions in Array

Given an integer array nums, return the number of reverse pairs. A reverse pair is a pair (i, j) where i < j and nums[i] > 2 * nums[j].

Examples
Input: [1,3,2,3,1]
Output: 2
Hints

Count Inversions in Array

Given an integer array `nums`, return the number of reverse pairs. A reverse pair is a pair (i, j) where i < j and nums[i] > 2 * nums[j].