Split String into groups with specific length

Question

How can I split the given String in Swift into groups with given length, reading from right to left?

For example, I have string 123456789 a

Answer 1

Another solution using substrings:

func splitStringByIntervals(str: String, interval: Int) -> [String] {

   let st = String(str.characters.reverse())
   let length = st.characters.count  
   var groups = [String]()

   for (var i = 0; i < length; i += interval) {
       groups.append((st as NSString).substringWithRange(NSRange(location: i, length: min(interval, length - i))))
   }

   return groups.map{ String($0.characters.reverse())}.reverse()
}

The output for :

for element in splitStringByIntervals("1234567", interval: 3) {
   print(element)
}

is:

1
234
567