Yes, in description we should have a point about that we will have invalid zipcodes for input

Mostly trial and error using the web-gui.
One way to make make the thinking slightly easier is a few properties of the problem.

1. You only need to find how to turn on the middle light, a diagonal corner light and a middle corner light. Then you can rotate the solutions to get all of the combinations.
2. If you keep track of button presses to get to a specific light combination, you can add two such combinations and do a modulus(2), on all numbers to get a new minimum number of presses to get to the combinations of light switches.

It is a little hard to describe in text though. I recomend pen and paper.

Good!

The tests are not broken. I tried many solutions and they worked fine.
Please read this and correct your code and it should pass:
https://www.geeksforgeeks.org/using-namespace-std-considered-bad-practice/.

Not a kata error: I tried many solutions and they worked fine.
Please see below my answer to your previous post.

when some c++ wizard like you ports it to c++. :)