title: return n indices of non-identical nearest neighbor vectors
body: <p>In a set of D dimension vectors, the nearest neighbor algorithm can efficiently acquire the n nearest neighbors for each vector in the entire set. </p>
  
  <p>However, in such set, if there are multiple identical vectors, the nearest neighbor algorithm will return the identical vectors as the nearest vectors first. This makes sense, because the identical vectors are always closer to each other than the non-identical vectors. </p>
  
  <p>But is there a algorithm just like nearest neighbor search, that does not take the identical vectors into account?</p>