K-means

代码说明：

   K均值算法描述： 给定类的个数K，将N个对象分到K个类中去， 使得类内对象之间的相似性最大，而类之间的相似性最小。(K-means algorithm described: a given number of classes K and N objects assigned to the K-th class, so that objects within the class of the similarity between the maximum, while the similarity between the minimum class.)