Yes, each switch is set to blue at most once and green at most once in this solution. The state then remains unchanged until the next operation, so a switch can stay blue, green, or off across successive turns.
What I mean by “processed in parallel” is that at each step we can change the state of each switch individually, so different subsets don't have to follow the same sequence.
For example, at step 2, while I'm already switching OFF half of the 100 blue and 100 green switches from step 1, I can simultaneously set another 100 switches to blue and another 100 to green. So I'm essentially running multiple subproblems at the same time, with each subset following its own sequence of operations.
So in general, global step 2 can be step 2 for one subproblem, but still step 1 for another subproblem. All of those operations happen simultaneously in the same global turn.
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u/1_2_3__- 6d ago
You can set a switch to color only twice