slightly different but same idea

Makes my code looks like spaguetti

Great job with the pop idea. Elegent!

Could you elaborate on what the lambda function does in your solution exactly?

This is the only right way to solve the problem. Nice job!

This is clear, concise and fundamentally solving the problem in an obviously efficient way. In short, a revelation.

Thanks. Your description is very helpful!

brilliant

Actually the method you are using can be extracted to a simple word: "stack" ^^
And it's really useful and clever, thanks a lot!

For me this is a genius solution!

The values 0, [], "", False and None are falsy in a boolean expression, in this case if new_plan means len(new_plan) != 0.

Well done! Bravo!