Problem - Count Smaller After Self

Given an integer array nums, return an array where counts[i] is the number of smaller elements to the right of nums[i]. Example: nums $= [5, 2, 6, 1]$ returns $[2, 1, 1, 0]$. You solved this with segment trees. The BIT solution is cleaner:

$1.$ Coordinate compress

$2.$ Process right to left

$3.$ For each element: query prefix count, then update Constraints: up to $10^5$ elements.