http://c.biancheng.net/cpp/view/6998.html
http://www.cnblogs.com/ggjucheng/archive/2013/01/13/2858470.html
http://www.cnblogs.com/xuxm2007/archive/2011/10/20/2218846.html
http://www.cnblogs.com/suyang/archive/2008/05/18/1201990.html
原文：http://www.cnblogs.com/karappo/p/5444615.html