论文：Elkan, C. (2003). Using the triangle inequality to accelerate k-means. In Machine Learning, Pro-
ceedings of the Twentieth International Conference (ICML 2003), August 21-24, 2003, Washing-
ton, DC, USA, pages 147–153.
参考博客：http://www.cnblogs.com/bradleon/p/6842549.html?utm_source=itdadao&utm_medium=referral
今天的任务，把这个原理搞清楚，最好代码写出来~
网上介绍了《数据挖掘导论》，很不错的书，有空看看。
改进后的k-means:
