code: func newAlphabet(s string) alphabet {
  	abc := dedupe(strings.Split(s, ""))
  
  	if len(abc) != 57 {
  		panic("encoding alphabet is not 57-bytes long")
  	}
  
  	sort.Strings(abc)
  	a := alphabet{
  		len: int64(len(abc)),
  	}
  	copy(a.chars[:], abc)
  	return a
  }
docs: // Remove duplicates and sort it to ensure reproducability.