http://blog.csdn.net/chief1985/archive/2007/12/19/1952931.aspx
http://21nw.com/2009/04/20/%E5%90%AF%E5%8F%91%E5%BC%8F%E6%90%9C%E7%B4%A2%E4%B8%8E%E6%8E%A8%E7%AE%B1%E5%AD%90/
http://notabdc.vip.sina.com/Solver/soko.htm
http://codecola.net/sps/index.php