说明：  K最近邻(k-Nearest Neighbor，KNN)分类算法，是一个理论上比较成熟的方法，也是最简单的机器学习算法之一。该方法的思路是：在特征空间中，如果一个样本附近的k个最近(即特征空间中最邻近)样本的大多数属于某一个类别，则该样本也属于这个类别。
(K-nearest neighbor (KNN) classification algorithm is a relatively mature method in theory and one of the simplest machine learning algorithms. The idea of this method is: in the feature space, if most of the k nearest samples belong to a certain category, then the samples also belong to this category.)