text: /**
   * @file methods/dbscan/random_point_selection.hpp
   * @author Ryan Curtin
   *
   * Randomly select the next point for DBSCAN.
   *
   * mlpack is free software; you may redistribute it and/or modify it under the
   * terms of the 3-clause BSD license.  You should have received a copy of the
   * 3-clause BSD license along with mlpack.  If not, see
   * http://www.opensource.org/licenses/BSD-3-Clause for more information.
   */
  #ifndef MLPACK_METHODS_DBSCAN_RANDOM_POINT_SELECTION_HPP
  #define MLPACK_METHODS_DBSCAN_RANDOM_POINT_SELECTION_HPP
  
  #include <mlpack/prereqs.hpp>
  
  namespace mlpack {
  namespace dbscan {
  
  /**
   * This class can be used to randomly select the next point to use for DBSCAN.
   */
  class RandomPointSelection
  {
   public:
    /**
     * Select the next point to use, randomly.
     *
     * @param * (point) Unused data.
     * @param data Dataset to cluster.
     */
    template<typename MatType>
    size_t Select(const size_t /* point */,
                  const MatType& data)
    {
      // Initialize the length of the unvisited bitset.
      size_t size = data.n_cols; // Get the size of points.
      if (unvisited.size() != size)
        unvisited.resize(size, true); // Resize & Set bitset to one.
  
      // Count the unvisited points and generate nth index randomly.
      const size_t max = std::count(unvisited.begin(), unvisited.end(), true);
      const size_t index = math::RandInt(max);
  
      // Select the index'th unvisited point.
      size_t found = 0;
      for (size_t i = 0; i < unvisited.size(); ++i)
      {
        if (unvisited[i])
          ++found;
  
        if (found > index)
        {
          unvisited[i].flip(); // Set unvisited point to visited point.
          return i;
        }
      }
      return 0; // Not sure if it is possible to get here.
    }
  
   private:
    // Bitset for unvisited points. If true, mean unvisited.
    std::vector<bool> unvisited;
  };
  
  } // namespace dbscan
  } // namespace mlpack
  
  #endif
  