problem493

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493. Reverse Pairs (Hard)

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 * 104
• -231 <= nums[i] <= 231 - 1

Related Topics

[Binary Indexed Tree] [Segment Tree] [Array] [Binary Search] [Divide and Conquer] [Ordered Set] [Merge Sort]

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