http://blog.csdn.net/dm_vincent/article/details/7655764
http://baike.baidu.com/link?url=hVNznQ8iLKukcj5K5FH2_FhDm5i-mHw87sOsUqnSnYUVX6unqx4EfzE_4XOwBvHfYZyQS9tf-Kfm-Fin2zTct_#5
并查集（Union/Find）
原文：http://www.cnblogs.com/bendantuohai/p/4560577.html
