Revenge of the Pancakes

Design a hardware module that flips pancakes to achieve the desired pattern. Given a string of plus and minus representing pancake orientations, determine the minimum number of flips needed where each flip reverses a prefix and toggles all orientations in that prefix.

Example: For "-" (one pancake facing down), flip all to get "+". Output: 1 flip.

Source: Google Code Jam 2016 Qualification Round - Problem B: Revenge of the Pancakes