Leetcode 3509. Maximum Product of Subsequences With an Alternating Sum Equal to K

Find a non-empty subsequence (order preserved) whose alternating sum (+,-,+,...) equals k and whose product is maximized but does not exceed limit. The core challenge is a DP/knapsack-style search that tracks subsequence parity for alternating-sum constraints and feasible products (bounded by limit) to maximize the multiplicative objective.