I have a solution that involves moving back and forth across the loop. You pick a starting point, car 0, and move +1 car right and ensure the light is on, then go left to car −1 and ensure the light is off; then go to car +2: ON, car −2: off, etc.
The first time you travel more than half way around the loop, you’ll toggle a switch from the “other branch”, which you’ll then discover when you reverse. That will allow you to compute the total size of the loop.
I have a solution that involves moving back and forth across the loop. You pick a starting point, car 0, and move +1 car right and ensure the light is on, then go left to car −1 and ensure the light is off; then go to car +2: ON, car −2: off, etc.
The first time you travel more than half way around the loop, you’ll toggle a switch from the “other branch”, which you’ll then discover when you reverse. That will allow you to compute the total size of the loop.