That's because Character is very, very different from ASCII in Swift (a character in Swift holds an extended grapheme cluster. See https://developer.apple.com/reference/swift/character). I also doubt the way they compute its ASCII value is optimal:

  extension Character {
    var asciiValue: UInt32? {
        return  String(self)
            .unicodeScalars
            .filter{$0.isASCII}
            .first?
            .value
    }
  }

Certainly if it is optimal, but probably also if it isn't, I would change the program to not do that conversion in inner loops.

Replaced String with Int array

https://gist.github.com/rookie/3d9a848c6fefacc4254da921da79b...