What do you mean by "optimization"?
Both .description and String() work the same way for integers - String initializer, Integer description

Edit:
Oh, I've noticed what you meant - number.description.sorted {...}? Not sure about optimization, but easier to read for sure.

Swift translation please review.

Swift translation please review

Swift translation please review :)

You are welcome :)

Well, no. $N values are values inside the closure. To access start or end just use start and end inside the closure.

If there are a single parameter inside the closure, only $0 will be available. As an example - .filter(...) could be written as:

return (start...end).filter { item in !String(item).contains("5") }.count

With this you can't access parameters with $0, but can with it's name - item.

For example .sort(...) method uses 2 parameters inside, so this:

(start...end).sorted { $0 > $1 }

Is the same as this:

(start...end).sorted { left, right in left > right }

I guess it will be easier to understand if you read about Shorthand Argument Names at: Swift Book

Yup, every $N parameter is a parameter inside the closure.

$0 represents a first parameter passed to the closure.
If you switch .filter with the for item in (start...end), then $0 would represent an item parameter, not start.

So $0, $1 and so on represent a parameters withing a closure scope.

I've translated this kata to swift: https://www.codewars.com/kumite/582edc8c2029ea0319000116, please review

I've translated this kata to Swift, please review: https://www.codewars.com/kumite/582da07f5f867798b3000353

I've translated this kata to Swift: https://www.codewars.com/kumite/582d9d9906e37fe2f8000c97, please review

I've translated this kata to Swift, please review: https://www.codewars.com/kumite/582d9b702de6d9a412000158

Sure, when i got the time :)
There are a lot of stuff going on lately.

Updated :)

I've made a translation for this Kata to Swift: http://www.codewars.com/kumite/58170668ca72bac0b6000087 please review :)