#493

Reverse Pairs

master · 1875 · lc hard +32 · verified · 33.8% accepted · 6,974 likes · top 11%

⚑ Fenwick Tree (Binary Indexed Tree)⚑ Coordinate Compression ⚑ Merge Sort / Inversion Count

Description

Given an integer array nums, count the number of important reverse pairs. A pair (i, j) is a reverse pair when i < j and nums[i] > 2 * nums[j]. Return the total count.

Example 1:

Input: nums = [1,3,2,3,1]

Output: 2

Explanation: The reverse pairs are:

(1, 4) --> nums[1] = 3, nums[4] = 1, 3 > 2 * 1

(3, 4) --> nums[3] = 3, nums[4] = 1, 3 > 2 * 1

Example 2:

Input: nums = [2,4,3,5,1]

Output: 3

Explanation: The reverse pairs are:

(1, 4) --> nums[1] = 4, nums[4] = 1, 4 > 2 * 1

(2, 4) --> nums[2] = 3, nums[4] = 1, 3 > 2 * 1

(3, 4) --> nums[3] = 5, nums[4] = 1, 5 > 2 * 1

Code

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class Solution:
    def reversePairs(self, nums: List[int]) -> int:

class Solution:
    def reversePairs(self, nums: List[int]) -> int: