Given an integer array nums, return the number of reverse pairs in the array.
A reverse pair is a pair (i, j) where 0 <= i < j < nums.length and nums[i] > 2 * nums[j].
Example 1:
Input: nums = [1,3,2,3,1] Output: 2
Example 2:
Input: nums = [2,4,3,5,1] Output: 3
Constraints:
1 <= nums.length <= 5 * 104231 <= nums[i] <= 231 - 1