Leetcode 3672. Sum of Weighted Modes in Subarrays

Given an array and a weight rule, compute the sum of each subarray's weighted mode (the most frequent element in the range, with ties resolved as specified) across either all subarrays or many query ranges. The core challenge is maintaining the current mode under range updates efficiently—using frequency maps plus order-statistics structures or offline techniques like Mo's algorithm—to avoid brute-force O(n^2) enumeration.