说明：   实现一个简单的密码生成系统。一个有效的密码由L(3<=L<=15)个小写字母(来自传统的拉丁字母集 a ... z )组成，至少有一个元音字母( a , e , i , o 或者 u )，至少有两个辅音字母(除去元音以外的字母)，并且按字母表顺序出现(例如， acd 是有效的，而 dac 不是)。 给定一个期望长度L和若干个小写字母，写一个程序，打印出所有的长度为L、能由这些字母组成的有效密码。密码必须按字母表顺序打印出来。
(Implement a simple password generator system. A valid password from the L (3 < = L < = 15) lowercase letters (from the Latin tradition set ' a' ...' z' ) composed of at least one vowel (' a' , ' e ' ,' i ' ,' o ' or' u ' ), at least two consonants (except for letters other than vowels), and appear in alphabetical order (for example,' acd ' is valid, but' dac ' is not.) Given an expected length L and a number of lowercase letters, writing a program that prints out all of the length L, can be effective by these letters of the password. Password must be printed in alphabetical order.)