Reverse Pairs
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.lengthnums[i] > 2 * nums[j]
Example 1
Input
nums = [1,3,2,3,1]Output
2The reverse pairs are
(1, 4) and (3, 4), where nums[i] = 3, nums[j] = 1, and 3 > 2 * 1.Example 2
Input
nums = [2,4,3,5,1]Output
3The reverse pairs are
(1, 4), (2, 4), and (3, 4), each satisfying nums[i] > 2 * nums[j].Constraints
- 1 <= nums.length <= 5 * 10^4
- -2^31 <= nums[i] <= 2^31 - 1