I daresay this is the solution. It is the most succinct and clear transformation of one data shape to another.

Smart usage of center - cool trick!

Agreed, while cleaver the longer term readability of this method seems to be less than ideal.

This is a clever way of using recursion to make this a one-liner, but at the cost of veryfying initial conditions (which may end up in -1) every time ball bounces :(

first try - did well , yet still learning how this env works.

THis is why the ruby standard library is so fantastic!

I see. Thank you!

It's because if you type something non-spoiler in a solution, people can see it on the dashboard.

do I use a spoiler flag on solutions? this is not a discourse. I did it anyway.

Use spoiler flag, please.

But I think complexity is n^2...