I didn’t ‘know’ that technique and still managed to work it out - and enjoyed the process, so it’s not so weird. Also I now have a driver to learn more about it!

I think idea was to lure lazy thinkers like me into an easy brute force solution for part one, and only have to do the maths for part two.
I guess if you started with the maths, part two was trivial.

Ha ha, I did that on day 10 too!

I realised just checking the initial route would have limited it just after I’d set the long task running to check all of them and didn’t want to break into it!

I also resorted to slow and brute force for part 2. There must be a clever elegant answer possible.