Method: Upwords::Player#cpu_move

Defined in:
lib/upwords/player.rb

#cpu_move(board, dict, batch_size = 1000, min_score = 0) ⇒ Object

Execute a legal move based on a predefined strategy

Basic strategy:

  • Find all legal move shapes and all possible letter permutations across those shapes (this computation is relatively quick)

  • Retun the highest score from permutation that do not produce in any illegal new words (this computation is slow…)

  • To speed up the above computation: + Only check a batch of permutations at a time (specified in ‘batch_size’ argument) + After each batch, terminate the subroutine if it finds a score that is at least as high as the given ‘min_score’ + Decrement the ‘min_score’ after each batch that does not terminate the subroutine to prevent endless searches

TODO: refactor the the ‘strategy’ component out of this method, so different strategies can be swapped in and out



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# File 'lib/upwords/player.rb', line 135

def cpu_move(board, dict, batch_size = 1000, min_score = 0)
  possible_moves = self.legal_move_shapes_letter_permutations(board)      
  possible_moves.shuffle!
  
  top_score = 0
  top_score_move = nil
  
  while top_score_move.nil? || (top_score < min_score) do
    
    # Check if next batch contains any legal moves and save the top score
    ([batch_size, possible_moves.size].min).times do
      move_arr = possible_moves.pop
      move = Move.new(move_arr)

      if move.legal_words?(board, dict)
        move_score = move.score(board, self)
        if move_score >= top_score
          top_score = move_score
          top_score_move = move_arr
        end
      end
    end
    
    # Decrement minimum required score after each cycle to help prevent long searches
    min_score = [(min_score - 1), 0].max
  end
  
  top_score_move
end