“Next best action” is a popular decision-making strategy. But how to define the “best” next action? This challenge may demonstrate it. Consider an NxN grid of lightbulbs. We are given an initial state where some of the bulbs are off and some are on. Then, at every step you need to choose a bulb in the off state. It will turned on, and every other bulb in the row and in the column of the bulb will be toggled: If it was on, it turns off, and vice versa. The goal is to reach a grid where all the light bulbs are on. Link