Leetcode 3404. Count Special Subsequences

Count the number of length-4 subsequences (p<q<r<s) with q-p, r-q, s-r >= 2 such that nums[p]*nums[r] == nums[q]*nums[s]. The core challenge is efficiently counting equal pairwise products across index splits while respecting the required spacing (n ≤ 1000, nums[i] ≤ 1000).