codewars/go/kyu5/not_very_secure/k.go

package kata

func alphanumeric(str string) bool {
	if len(str) == 0 {
		return false
	}
	for _, r := range str {
		if !((r >= '0' && r <= '9') ||
			(r >= 'A' && r <= 'Z') ||
			(r >= 'a' && r <= 'z')) {
			return false
		}
	}
	return true
}