http://nosql.mypopescu.com/post/1123347183/redis-implementing-auto-complete-or-how-to-build-trie
http://www.paitoubing.cn/blog/php-trie-mmseg
http://www.cnblogs.com/cherish_yimi/archive/2009/10/12/1581666.html
http://www.cnblogs.com/cherish_yimi/archive/2009/10/12/1581795.html