I like it

I think this is a more general solution to process string vs using "replace"

Can anyone explain me how come empty arrays are removed at second and beyond level, please? Because "[] as? [Any] -> []", it's not nil to be removed by flatMap.

Empty arrays are not in the challenge. That said, it was an interesting challenge to address.

The reason some are removed is the flattening logic removes and second level and beyond empty arrays.

To remove the first level empty arrays, add a filter to the return value:

.filter { !(($0 as? Array<Any>)?.isEmpty ?? false) }

neat like a groom's bow tie

funny factorial )

looks awesome! I would appreciate if you shared the name of that function/solution if there is one. thanks in advance

thanks, i learn something new from this. It's my first time to use a sequence function with defer inside.

Why difference * 2?

beautiful

String(num).compactMap { Int(String($0)) }.reversed() in new version of Swift

Nice.

not sure if recursion is the best approach here, since you do abs each time, although it will be a valid value after the first execution