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Practice Reverse Pairs

Read the task, work through the examples, and check your approach against the constraints. Use the original LeetCode task for coding and submissions.

Hard#493
LeetCode Problem

Reverse Pairs

ArrayBinary SearchDivide and ConquerBinary Indexed TreeSegment TreeMerge SortOrdered Set

Problem Statement

Count index pairs (i, j) in nums with 0 <= i < j < nums.length and nums[i] > 2 * nums[j]. The comparison is strict and uses twice the later value, not merely nums[i] > nums[j].

Source: Reverse Pairs on LeetCode. Use the original task for its coding environment and submissions.

Examples

# 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 * 10^4
-2^31 <= nums[i] <= 2^31 - 1

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