You are given an integer array, nums. Your task is to count how many reverse pairs exist in the array and return the total number of such pairs.

Constraints:

• $1 \leq$ nums.length $\leq 5 \times 10^4$

• $-2^{31} \leq$ nums[i] $\leq 2^{31} - 1$

Let’s take a moment to make sure you’ve correctly understood the problem. The quiz below helps you check if you’re solving the correct problem:

We have a game for you to play. Rearrange the logical building blocks to develop a clearer understanding of how to solve this problem.

Implement your solution in the following coding playground.