Leetcode 3420. Count Non-Decreasing Subarrays After K Operations

Count how many subarrays can be turned non-decreasing with at most k +1-increment operations, where the minimal cost for a subarray is the sum of deficits needed to raise each element up to the previous (max(0, prev - curr)). The core challenge is to compute these costs for all subarrays efficiently (n up to 1e5), typically with a sliding-window / two-pointer approach that maintains the cumulative required increments.