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
}
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
}
// Remove duplicates and sort it to ensure reproducability.