Fantastic puzzle. Took me ages to realise the twist though, because I was somehow set on making them oscillate further on every iteration and couldn't understa

Fantastic puzzle. Took me ages to realise the twist though, because I was somehow set on making them oscillate further on every iteration and couldn't understand how I was to remember how far I went without a stack. Basically what I wanted to do was: x left, if its not there, return. Next time x * 2 left, return to base if its not there, ...