func UniqueStrings(slen uint, n int) (ss []string) {
	exist := make(map[string]struct{})
	ss = make([]string, 0, n)
	for len(ss) < n {
		s := randString(slen)
		if _, ok := exist[s]; !ok {
			ss = append(ss, s)
			exist[s] = struct{}{}
		}
	}
	return ss
}
func UniqueStrings(slen uint, n int) (ss []string) {
	exist := make(map[string]struct{})
	ss = make([]string, 0, n)
	for len(ss) < n {
		s := randString(slen)
		if _, ok := exist[s]; !ok {
			ss = append(ss, s)
			exist[s] = struct{}{}
		}
	}
	return ss
}
// UniqueStrings returns a slice of randomly generated unique strings.