http://www.cnblogs.com/chinazhangjie/archive/2010/10/22/1858410.html回溯法
http://www.cnblogs.com/chinazhangjie/archive/2010/11/01/1866136.html分支限界法
http://www.cnblogs.com/chinazhangjie/archive/2010/10/22/1858410.html回溯法
http://www.cnblogs.com/chinazhangjie/archive/2010/11/01/1866136.html分支限界法