有向图相关的内容

http://www.cnblogs.com/SadGeminids/archive/2011/11/09/2243544.html

http://my.oschina.net/u/247728/blog/76200

http://hi.baidu.com/sunnyykn/item/c40e9217d311b0443a176efb

http://blog.csdn.net/kay_sprint/article/details/6957336

http://www.cnblogs.com/uniquews/archive/2012/02/23/2364627.html