http://blog.sina.com.cn/s/blog_64d9a6ef0101ghvs.html
http://blog.sina.com.cn/s/blog_49cd89710102v3b1.html
https://zhuanlan.zhihu.com/p/24069545
http://www.cnblogs.com/tuitui1989/p/5331113.html
http://dblab.xmu.edu.cn/blog/1297-2/
https://my.oschina.net/snug/blog/664932
http://www.cnblogs.com/tuitui1989/p/5331113.html
http://www.tuicool.com/articles/fANvieZ 协同过滤