http://www.cppblog.com/mythit/archive/2009/04/19/80492.aspx
http://www.gamedev.net/page/resources/_/technical/artificial-intelligence/a-pathfinding-for-beginners-r2003
http://blog.csdn.net/feixiaoxing/article/details/6982932
http://www.codeproject.com/Articles/4391/C-A-Star-is-born
http://download.csdn.net/detail/ysg8422am/1929986