Minimum Operations to Convert All Elements to Zero

Given a nonnegative integer array, each operation picks a contiguous subarray and sets all occurrences of the minimum value in that subarray to 0; compute the minimum number of operations to make the whole array zero. The core challenge is deciding optimal subarray choices (equivalently counting merged "layers" of values), typically solved by divide-and-conquer on minima or a monotonic stack that tracks and merges value segments.